A 2.26kΩ, 1%-precision resistor with 5 color bands (E96 series), from top, 2-2-6-1-1; the last two brown bands indicate the multiplier (×10) and the tolerance (1%).
An electronic color code is a system which wordlessly identifies either the functions of cables and connections, or the types and variants of electronic components. Codes for cables and connections range from the use of pink, blue, and green connectors on computer sound cards, to early attempts at standardizing the colors of battery, loudspeaker, and antenna wires of radio sets in the 1920s, to the 25-pair color code, used in telecommunications cables. Among the component identification applications, those used on resistors are most widespread, with usage on inductors also popular, while in the past, many variations were applied to capacitors, diodes, and other part types.
History
RMA resistor color code guide, ca. 1945–1950Computer components marked with color bands; resistors with beige background, inductors with turquoise, and capacitors with greenish and yellowish backgrounds.
Before standardization, some manufacturers used their own color codings on the fixed resistors in their radio sets, seemingly choosing a random color for each part stock number. Then, in 1930, a new code started coming into wide usage among radio makers. This new style encoded the resistance value of each part by means of one background paint color and usually, two additional paint marks. The Radio Manufacturers Association (RMA) gave its endorsement of this coding around 1931. This all-over painted, "body-end-dot" coding style, while most vividly associated with pre-war radio equipment, did live on for a while, and was still in use in the 1960s.
In 1935, advertisements appeared for resistors coded with a sequence of color bands including one acting as a tolerance indicator; the RMA adopted a standard for this alternative style by 1941. A 1943 reference book, Mechanical Practice gives an early description of a further development. While the 1935 banded style only called for two digit bands before the band that specifies a "multiplying value", coded as an exponent, the new variation had three, bringing the total number of bands including the tolerance to five, as opposed to just three or four. This might seem to indicate that even at that early date, the use of a four–five rule became necessary in decoding banded resistors; in going from four to five in the total count of bands, that is where the number of digit-encoding bands increases from two to three, moving the exponent band from the third to the fourth position. In practice this was not a very important rule to memorize back then, as actual resistors showing the three-digit coding innovation remained scarce for twenty years afterwards. Eight decades later, application of the rule in some form is routinely required, but now a big part of the art of reading random-sourced resistors is, recognizing the exceptions, those tricky cases where resistance codings do not follow the rule.
Over many decades, as the organization name changed (RMA, RTMA, RETMA, EIA) so was the name of the code. Though known most recently as EIA color code, the four name variations are found in books, magazines, catalogs, and other documents over more than 95 years.
In 1952, the International Electrotechnical Commission (IEC) published a fork of the RMA's banded resistor concept as IEC 62:1952; although it did not expand to include three-digit codings following a four–five rule until the 1974 edition, its successors and national versions/translations are widely referenced today. Starting with the 1968 edition it added in the widely used "RKM codes" for printed text component values on resistors and capacitors. Successive revisions, up to the current IEC 60062:2016, added more optional features to the resistor color code, but also diverged from the EIA versions.
One standardized color code scheme for capacitors was in use by 1934, although some radio makers kept using random-picked color codes on these longer than they did on resistors. (At that point, most were still calling these "condensers", an older term.) There were many variations of flat postage stamp/domino-style mica and paper dielectric capacitors with paint dots; tubular capacitors with a sequence of spots or bands also date to the 1940s. Eventually many more styles were produced using mica, paper, ceramic, glass, and plastics for the dielectric, also many tantalum types, not all codings directly published by the RMA and successors, some with dots, some with bands, some with layer-dipped paint. A 1949 article detailed nine marking types in use by that time, but the proliferation of styles was just getting started then. Some later ceramic-dielectric ones from the VCR era of roughly 1980 onward look a lot like modern small axial-leaded resistors. Today, while color-coded "caps" are less commonly encountered, the layer-dipped "tropical fish" ones are still preferred by some, and recent reproductions of certain old tubular capacitor types have been embellished with replica "bumble-bee" color bands, suitable to make any classic-style electric guitar more authentic.
Schemes for color-coding small inductors, (A.K.A. radio frequency chokes, coils, etc.) were in use by 1950; as with the capacitors, some types do look a lot like modern small resistors. For reading, while many recent ones decode like common resistors, giving an inductance value in microhenries, older ones and some current ones are more complicated; unlike resistors, a gold or silver band may be at either end, or both, and there may be no exponent band.
Small semiconductor diodes/rectifiers were being marked with color bands by 1958. Some Zener/avalanche-breakdown diodes have paint bands that indicate their main characteristic of interest, which is, their nominal rated Zener voltage. More commonly, a type number is indicated using one of several variants that support the U.S. JEDEC "1N" series (Glass diodes marked this way were common in the 1960s.) and European Pro Electron numbering schemes. Proprietary arbitrary codings were used by some; Hitachi made diodes with bands of designer colors such as "verdure" and "yellow ocher". Many later-production glass diodes have only one or two color bands, indicating a broad type category.
Several complex color coding systems for plastic-cased transistors were in use in the Soviet sphere. The U.S. standard for diodes allows application to transistors but seems to have been little used for this. Usually when color markings are found on U.S.-style small plastic transistors that have printed numbering also, they indicate a bin-sort code or something proprietary.
By 1970, disc-shaped thermistors and voltage dependent resistors/varistors were being made with color coding in the form of layer-dipped paint; these may be confused with some ceramic disk capacitors which are painted similarly. There are also tubular, axial-leaded styles of varistors which have their own look which differentiates them from other components.
There is even a color band coding standard for fuses, published in 1988 as IEC 127, and adopted in national variants covering both cartridge types that look like fuses and also, miniature types that look like modern small resistors.
The paint pigment used for the number seven, according to some British sources, is supposed to be a "dark violet"; others in the British Commonwealth have called it mauve. The general consensus of references world-wide through the decades would be a simple violet, although, in the early years there are several sources that call it purple, and even a vote for lavender may be found.
Compared to identification by printed codes, the color band system is optimized for reading from multiple directions, independent of rotation of the part. This may explain why variants of it remain in wide use on tiny surface mount packages of the leadless cylindrical, or "MELF", type, which do not have a top or bottom. But the color set, chosen with no regard for accommodating common types of color blindness, is seen as a major disadvantage. Some people may fault the system itself for difficulties caused by manufacturers' sloppiness, such as not making the orientation obvious, an unfortunate background color choice, or not using good, well-chosen paints for the bands. Sometimes, even without factors such overheating or dirt accumulation on the part, and viewed by a person with normal color vision, one manufacturer's orange may match another's brown.
Resistors
One decade of the E12 series (there are twelve preferred values per decade of values) shown with their electronic color codes on resistorsA 0Ω resistor (zero ohm), marked with a single black band
The resistance value is given by two or three color markings (usually rings/bands starting at the head end, or rarer, partial bands or spots, or, in the oldest style, the body/background and optional end mark) indicating numeric digits plus one more giving a "multiplying value" which is specified by an exponent. The multiplying value is ten raised to the power of the exponent; for the nine positive valued colors that is just a one followed by zeroes. After the exponent, a tolerance indicator band and sometimes one more may follow, making up to six bands in total. The system is similar to scientific notation, but it differs in its normalization rules. In the normalized scientific notation representation of any number, the first nonzero digit is the "units," or "ones" place. A denormalized case, where some other position is the first nonzero digit, may often be encountered in the intermediate steps required when adding or multiplying two numbers, before the final step of re-normalizing. But in resistor coding, the first nonzero digit is the tens or hundreds place, depending on whether there are two or three digit bands, with exceptions of some low-end resistance values. These exceptions, where the sequence starts with black/zero, are the denormalized resistor codings, used when the lowest available color for the exponent is not low enough otherwise.
For example, the number fifty-six thousand is in normalized scientific notation. A 2% tolerance resistor of that many ohms, not nearly low enough to need a black first band, may be coded with two or three digit bands; it may read:
with markings green(5)-blue(6)-orange(3)-red(2%) or,
with markings green(5)-blue(6)-black(0)-red(2)-red(2%).
This gives the two equivalent parts different colors for their exponent bands. Doing a rough sort of mixed resistors might involve using a row of jars, with one jar for each exponent color (third band) of the two-digit coded resistors, and also a second row with a jar for each exponent color (fourth band) of the three-digit coded ones. A 56000 ohm resistor might be then found in the 2 digit oranges or the 3 digit reds. The main difficulties in this process are getting the correct reading orientation on some of the smaller resistors, and, identifying each resistor as a two- or three-digit coding, to tell which row it goes in. If all the resistors were made conforming to the EIA and IEC standards, they would all follow the four–five rule, where four and fewer bands always imply there are two digit bands before the exponent, while five or more always mean there are three digit bands. In practice, many resistors will be found where the rule has been flouted or disregarded.
Many call the numeric digits given by the up-front color bands "significant digits", "significant figures", or, in the current IEC standard, "significant numerals". Pedants might argue that the word "significant" is misleading unless much arcane explanatory text is added, (this being almost never provided,) so it might be better to use a term like "numeric digits," "marked digits," or "coded digits" instead.
Some coding diagrams may be considered misleading, implying that a two-digit resistor is like a three-digit one that has lost its ones/units-digit, rather than correctly showing the hundreds digit being lost.
Some sources give graphic decoding keys that make it look like, in going from a four- to a five-band resistor, the new band is added as the middle position, and going from a five- to a four-band resistor, it is the middle one that is lost. These may foster the false presumption that a five-band resistor whose middle band is black, which decodes to zero, should have the same value as the four-band code obtained by rubbing out the black band.
The current IEC standards have no requirement to have any coordination between the tolerance band color and the choice to use 2 or 3 digit-coding bands. There have been attempts to enforce such a correspondence; the 1943 source Mechanical Practice opined that the 1% and even 2% tolerance indication should be permitted only for the 3-digit marking case, but this was never followed to any extent at the time. Eventually the IEC standards prescribed only the 2 digit practice for every supported tolerance including 1% until 1974. Typical current practice uses 3 digits for 1% or better, 2 digits for 5% and up; 2% tolerance may be found either way. Exceptions with 3 digit coding and a gold, 5% tolerance band can be found; sometimes this has been done in order to have a sixth solid band to indicate a temperature sensitivity specification by IEC practice. A gold or even silver tail-end band on a 3-digit, 5-band coding could result simply from following EIA RS-279 and RS-196-A, prescribing 3-digit coding on "film-type" resistors, or to mark a 1 gigohm resistor without needing to go beyond violet for the exponent band.
Color code markings are less likely to be used on resistors of very low or very high values, large power resistors, and very tight-tolerance parts, as these would be considered "specialty" rather than "commodity" products, with a need to print extra information. On Surface-mount technology PC boards, however, sometimes the more specialized resistors are the color-coded ones; a digital multimeter may contain a few color-banded precision types in the leadless "MELF" case surrounded by many typographically-marked "chip" type resistors.
Color sequence system
Orientation for reading
Resistors requiring varying degrees of finesse in identifying the correct reading orientation. Best viewed as a zoomable svg file
Reading color-sequence resistors requires first identifying the head and tail ends; decoding charts typically show a resistor with the head end at the left, so the code reads left to right. Difficulty of this task varies; the easiest case applies if, anywhere other than as the middle band of the sequence, there is at least one gold or silver band. This metallic-paint "Shiny" points out the tail end; it does not have to be the extreme end band, or even second from the end, and might not be the "tolerance band." The same applies to a pink, or salmon-pink band, if it is not just a faded violet. (If there is a Shiny at each end, or on both sides of the middle of the sequence, that is probably an inductor, misclassified as a resistor.)
If that fails, step two is to look for one of the more obscure, but still reliable and definitive, orientation indications. For old-style plastic-encased molded flat resistors with spots rather than bands, the type easily confused with vintage flat capacitors, there may be a molded-in arrow pointing from head to tail, and supposedly there are (rare, photo not available, but defined by IEC) resistors with five plain bands plus a dotted or interrupted sixth band; this indicates the tail. More commonly, there can be a single paint dot or broken band separating four solid bands from a fifth; this is also a tail end indication. If one of the inter-band gaps is widened to fit text characters or a logo, that also is a tail-end indication even if it separates three bands, at the head, from two more, at the tail.
If none of these apply, three less-foolproof clues based on band widths and spacing may have to be used, with finesse applied in case of a conflict.
The first clue is the margin test. Looking at the open margin space beyond the two ends of the color sequence, the closer, tighter end is suggested as the head. Ideally, this should be reliable in all cases regardless of the number of bands. (Or spots or broken bands, in some cases.) Pedants might argue that the IEC standard requires manufacturers to make this a sufficient and conclusive indicator, with no other clues needed, and if people would follow the rules, "That would be great." But some might object that this would take away much of the sport involved. Anybody could read all the resistors then! This test is pretty reliable for cases of three, and often four, bands not resolved above, but for small five- and six-band resistors, there are many sloppy ones out there where it is best to consider this a weak indication, potentially outweighed by one or both of the others, especially if the margin difference is small.
For the second clue, the gap test, if one of the inter-band gap widths exceeds all the others by a noticeable amount, and it is the gap next to one of the end bands, that can be a fair evidence of the tail end even if the gap doesn't have printing or a paint dot in it. Greater gap size implies a stronger evidence.
And thirdly, for the width test, on a five- or six-band resistor where one band is the widest by about 50% or more over all the others, this can be a tail end indicator if it seems to be following modern IEC conventions. This includes any six-band resistor where the wide band is an end band or second from the end, where this is strong evidence of that being the tail end. And, even on a five-band resistor with a small, modern-looking glossy, painted or epoxy body, having the wide band as one of the end bands, that is still a fair evidence of that being the tail end. A brown plastic background or terminal ends of the tube showing a different color or material are examples of resistors that are not "modern looking" and may instead have their head-end band widened. On some resistors following a long-established U.S. practice, a double-wide head-end band indicates a wirewound resistor.
Considering these three tests, if at least one of them gives a direction indication, and there is no conflict among them, that is a cause for celebration. Otherwise, the strengths of the three indications may have to be weighed, and there is still no guarantee that plain sloppy marking will not leave an ambiguity. A hybrid of the three clues may also be of value, where the two end bands are ignored, and the margin test done on the remaining (1 to 4) bands. Other arcane tests may help with some five-band resistors, especially those where the middle band is the only Shiny. If only one orientation gives a value and appropriate tolerance color according to the standard value lists, there may be a temptation to assume deviations from those lists cannot exist, but in practice, exceptions may be found which only give a standard value when read wrong/backwards.
Haphazardly marked 1 percent tolerance resistors with five rather evenly-spaced bands, centered on the part, are widely available in assortment packs. With these, there are worthwhile shortcuts that work on certain value ranges, like, if one end band of a resistor is not brown, that is the head, (This works for all values not starting with digit "1") and, for the under-10 megohm values common in low voltage work, if one of the second-from-the-end bands is a color value 5 or greater (green through white) that also indicates the head end. Some 1% standard-value codings are symmetrical and read the same either way; but also, two different standard-value resistors may be mirrorings of each other.
Decoding the value
Once the head end is identified, a code table or mnemonic gives a numeric equivalent for each of the bands that encode the value. For resistors known to be in strict accordance with IEC or EIA standards, decoding the value in ohms involves using the four–five rule to determine whether to take two or three digits from the bands at the head end, and then adjusting the resulting integer according to the exponent band which follows, at position three or four. For an exponent band of gold, silver, or pink, that means dividing by 10, 100, or 1000, respectively; these are the colors whose numeric value is negative. For the other exponent colors, it is just a matter of adding the indicated number of trailing zeroes, or, none for black.
A band following the exponent band specifies the tolerance rating; if only three-bands, 20% is generally assumed. An IEC-compliant three-digit resistor may encode a temperature sensitivity or temperature coefficient of resistance (TCR) rating, in units of ppm/K, with a sixth solid band, or a color dot or interrupted band on either side of the fifth solid band, or by a helical/diagonal mark crossing the five solid bands.
Here is an example of a two-digit, four-band resistor:
The first significant figure of component value (left side)
The second significant figure (some precision resistors have a third significant figure, and thus five bands).
The decimal multiplier (number of trailing zeroes, or power of 10 multiplier)
If present, indicates tolerance of value in percent (no band means 20%)
In the above example, a resistor with bands of red, violet, green, and gold has first digit 2 (red; see table below), second digit 7 (violet), followed by 5 (green) zeroes: 2700000ohms. Gold signifies that the tolerance is ±5%.
The standard color code per IEC 60062:2016 is as follows:
Standardized resistors follow various E series of preferred numbers for their specific values, which are determined by their tolerance. A surprising variety of additional random values may also be available from stock at major suppliers.
Exceptions to IEC practice; code sequence variations
There are many exceptions to the IEC/EIA prescribed sequence diagrams to watch for, some rare, some pretty common. These typically started out with someone deciding to take the four–five rule more like a suggestion. A five-band resistor, following the rule, and current IEC standards, is like a four-band one with an extra digit band, the hundreds place, added at the head end. But in many cases instead a band is added at the tail, to indicate a widely variable piece of gratuitous random information, making a five-band resistor with only two coded digit bands. It may be hard to figure out what this added band is saying, but a bigger problem is that on a random-sourced five-band resistor, presence or absence of a gratuitous fifth band re-defines all the other bands. A 1986 article details how, for example, a pair of identically-marked resistors with the fifth band of red could have two different values, if one is a 2% tolerance, three-digit part made according to IEC/EIA rules, and one is a two-digit resistor with red gratuitous fifth band. Many decoding keys do not see this issue as rating a mention.
Through the years, gratuitous fifth bands have been used to specify information such as a reliability rating, (yellow, orange, possibly other very rare ones, on brown plastic background, under old U.S. military spec.; made in the 1960s through 1997) or a lead solderability rating, (white or rare green, also per US military specs.) or a temperature sensitivity characteristic, or a "Grade 1 high-stability" attribute, (salmon pink according to U.K. standard "RIC/112", 1950s and 1960s; may fade to white) or an indication that the tolerance is by "total excursion". (colored as a repeat of the regular tolerance band, from the U.K. in the 1960s.)
The gratuitous fifth band may also specify the amperage and temperature rating of an internal thermal fuse on an "over temperature protector" resistor, or indicate some other attribute such as fusible in general, fusible wirewound, flameproof, flameproof fusible "failsafe" wirewound, fusible anti-explosion wirewound, high-voltage, anti-surge, fusible anti-surge, high-power (compact) wirewound, non-inductive wirewound, a "discharge path resistor," even high sound quality types for audiophiles. A mix of black, white, brown, red, orange, yellow, green, blue, and violet are all found on current active products. The specific example cited in that 1986 article involved a temperature sensitivity indicator band, which is now much less common as a gratuitous fifth, but, for example, a false-twin resistor pair with violet fifth bands can be readily obtained today. And possibly, a false twin of a common three-digit, 1% or 2% tolerance resistor might be found among recent two-digit parts with brown or red gratuitous fifth band, supplied by several manufacturers.
Resistors presenting various difficulty levels in separating the adherents and exceptions to the four–five rule implicit in IEC/EIA standards. Best viewed as a zoomable svg file
A strategy for classifying five-band resistors, into the standards-conformant three-digit and rule-breaking two-digit categories, may involve multiple clues. To start out, the two-digit with gratuitous-fifth case can be assumed for any with a (possibly faded) salmon-pink tail-end band or either Shiny or plain pink as the middle band. And, resistors with the old-style brown plastic casing and a silver or gold fourth band, go with the twos if the fifth band is orange or yellow; also blue, green, gray or violet if the first band is double-width. Any specimen where the last two bands are a matching pair of brown, red, orange, green, violet, gold, or silver is a possible total-excursion resistor. If these two are slightly thinner, and are separated from the first three by an (at least slightly) oversized gap, or especially if there is a "w" logo in the gap, that may be considered a confirmation of this type. These go with the twos.
Among resistors that can be excluded from being the total-excursion type, (any that do not have one of those color pairs, or that can be presumed not to be from the U.K. in the 1960s,) any that have a fourth band other than silver, gold, brown, or red can generally be assumed to be threes. And with them go any resistors having a random printed typographic code or a temperature sensitivity indicator color dot between the fourth and fifth bands, or with temperature sensitivity indicated with a helical/slash mark. For the leadless surface-mount cylindrical resistors, there are some two-digit ones with a gold fourth and yellow gratuitous fifth in a 3 by 9 millimeter size, unusually large for this type of package, but the rest of the known leadless five-band types are threes.
But now, due to running out of clues with quite a few possibly unresolved, it may be time start going by what is likely to be encountered, rather than what theoretically could exist. For one thing, putting any remaining ones having a black, yellow, or orange fifth band in with the twos should be safe except for rather rare, tighter-than-0.1%-tolerance resistors. The same might be said for white, of which many two-digit examples can be found, with the caveat that three-digit resistors with a white fifth for 0.02% tolerance are in a current Yageo product line and just might be found in precision equipment.
Specimens with a black third and gold fourth band decode to the same value either way, leaving only the tolerance in question. If only one of the two decoding schemes gives a standard value with an appropriate tolerance color according to the standard value lists, although not an infallible indication, this may be taken as a strong clue. For any remainders it might be helpful to have pictures showing the general look of some current-production gratuitous-fifth types such as Vitrohm's CRT series with brown, red, and orange, JEPSUN's and Firstohm's PPR and SSR series with red, Vishay's and Yageo's with violet, and a few vintage ones with a temperature sensitivity indicator or a green solderability indication as the gratuitous fifth.
Possible candidates for finding a gratuitous-fifth resistor with coding to match a very common three-digit, 1% tolerance resistor, with a brown fifth band, could include one from the Vitrohm CRT series; offered values include 120 ohms 5%, whose false twin would be a standard E96 value, 12.1 Ohms.
After discarding the fifth band, the gratuitous-fifth types decode their value and tolerance as a common two-digit four-band resistor, (However, see below in case of a white or gray exponent band...) but there is also an even more exotic five-band exception. Supposedly the Yageo-Vitrohm RXS series resistors, if under 0.1 ohms value, will be like an IEC-conformant four-band resistor except that one silver and one gold band replace the pink exponent band. With silver as the middle band color, these would not be confused with the normal three-digit type, but they may masquerade as a relatively normal gratuitous-fifth resistor of ten times their true resistance such as some of the Vishay-Draloric LCA series. (With their gold gratuitous fifth band, those too may have three Shinies in a row at their tail end.)
There are also cases where on a resistor with only four bands, the final one is a gratuitous addition to the IEC standard coding. Salmon-pink and yellow gratuitous fourth bands have sometimes been added to three-band resistors, positioned where a tolerance band is expected; other color examples may exist. These do not break the four–five rule, so they will not result in a false value reading.
Then is it safe to assume value coding exceptions will not be a problem on four-band resistors' values? Not really; there is another way to break the rule. Sometimes a four-band resistor may be like a three-digit five-band resistor with a suppressed/imaginary fifth band. The user is expected to know this is a special case, and that the missing/imagined tolerance band indicates maybe 1% rather than the traditional 20%. So a 56.2 ohm resistor could have the same coding (green-blue-red-gold, ) as a common two-digit, 5600 ohm 5% resistor. In current production this may be limited to the small leadless-type resistors used for surface mounting but in past years, it has been done on certain very small (about 4 millimeters in length) leaded ones too.
And what about cases of other than four or five bands? Supposedly Yageo may place a yellow, orange, violet or white gratuitous sixth band where IEC practice would only allow a temperature sensitivity code band; with no violation of the four–five rule, the resistance would still be read correctly. For three or fewer bands there are more special cases. On a three-band resistor with a gap after the first two, this may be the equivalent of a canonical 10 to 99 milliohm four-band resistor with the wide gap in place of the pink exponent band called for under the current IEC standard. This goes beyond just breaking the four–five rule, as it changes the meaning of the third band from the exponent to the tolerance. Also, on uninsulated black carbon composition resistors, old references say any black paint bands may be omitted, so the full sequence may need to be mentally reconstructed.
Zero ohm resistors, marked with one or sometimes two black bands, are lengths of wire wrapped in a resistor-like body which can be mounted on a printed-circuit board (PCB) by automatic component-insertion equipment. A coding of four black bands has been used for an arbitrary large, (such as anything over 100 kilohm) resistor meant for use as a core for winding an inductance.
More exceptions to IEC practice; color definition inconsistencies
Historically not every manufacturer has followed the current IEC coding chart for tolerance band colors and, for grey and white, even the exponent band colors, which are important to the decoded resistance result. A listing of these variations follows:
Table of exponent and tolerance color variations for resistors (large, hidden by default)
Color Name
Numeric value (Negative values apply to exponents only.)
Exceptions to numeric value sometimes found as exponent on resistors
Resistance tolerance percentage, according to various sources
1938 "Extended" code quoted in 1943's Mechanical Practice
Docs of U.S. military
Chart from Findlay 1959, widely reprinted in the '60s and '70s
EIA RS-279 (1963) and RS-196 (1970) for three-digit film resistors
Current IEC 60062 (2016)
Yageo Corp. precison resistor datasheet 2024
Coding published by Futaba Corp.
One Russian Language Source
High-voltage two-digit four-band resistor, per Vishay
Obscure British practice, c. 1950s
Likely meaning on two-digit resistor, inc. vintage parts
Likely meaning on three-digit resistor
None
–
−3
–
±20
±20
–
±20
±20
–
–
–
±20
±1
Pink
−3
–
–
–
–
–
–
–
–
–
–
–
–
Silver
−2
–
±10
±10
±10
±10
±10
±10
±10
–
±10
±10
±10
Gold
−1
–
±5
±5
±5
±5
±5
±5
±5
–
±5
±5
±5
Black
0
–
±20
±20
±20
–
–
±0.01
±0.005
–
±20
¯\_(ツ)_/¯
Brown
1
–
±1
±1
±1
±1
±1
±1
±1
–
–
±1
±1
Red
2
–
±2
±2
±2
±2
±2
±2
±2
–
±2
±2
±2
Orange
3
–
±3
±3
±3
–
±0.05
±0.02
±0.01
–
–
±3
±0.05
Yellow
4
–
±4
–
GMV
–
±0.02
±0.005
±0.02
±5
–
±5
±0.02
Green
5
–
±5
±5
±5
±0.5
±0.5
±0.5
±0.5
–
–
±5
±0.5
Blue
6
–
±6
±10
±6
±0.25
±0.25
±0.25
±0.25
±0.25
–
–
¯\_(ツ)_/¯
±0.25
Violet
7
–
±7
–
±12.5
±0.1
±0.1
±0.1
±0.1
±0.1
–
–
±7
±0.1
Gray/Grey
8
−3
±8
–
±30
±0.05
±0.01
±0.05
±0.05
±0.05
±10
–
¯\_(ツ)_/¯
±0.05 or ±0.01
White
9
−4;−3
±9
±2.5
±10
–
–
±0.02
–
–
–
±1
¯\_(ツ)_/¯
±0.02
Under current IEC or the early RMA standards, there should be nothing special about gray or white as the exponent band; gray means a resistance ten times the value of what it would be with violet, and white means ten times that. But documents of Yageo Corp. would make gray an alternate for IEC's pink, with white to be used on values too small for pink, for a numerical value of −4. And, Ohmite and at least one other manufacturer have used white for numerical exponent value −3, instead of IEC's pink. So, brown-black-gray could mean 1 gigohm or 0.01 ohm, and brown-black-white could be 10 gigohms or 0.01 ohm or 0.001 ohm.
To summarize the variations of the tolerance colors, only silver, gold, brown, and red have had their meanings unchanged since 1943, (on both two- and three-digit codings) and generally the rainbow colors beyond red will indicate a tolerance tighter than 1% on three-digit resistors, and looser than 2% on two-digit resistors.
As an aside, resorting to using an ohmmeter is always an option, but it gives different information than reading the color code does. It tells what the resistance is now; reading the code tells what it was supposed to be when it was new. To assess how well the part has aged, that takes both.
Body-end-dot system
The "body-end-dot" or "body-tip-spot" system was used for cylindrical composition resistors sometimes still found in very old equipment (built before the Second World War); the first band was given by the body color, the second band by the color of one end of the resistor, and the multiplier by a dot or band around the middle of the resistor. The other end of the resistor was in the body color, silver, or gold for 20%, 10%, 5% tolerance (tighter tolerances were not routinely used).
Examples
Example color-coded resistors
From top to bottom:
Green, blue, black, black, brown
560ohms ±1%
Red, red, orange, gold
22000ohms ±5%
Yellow, violet, brown, gold
470ohms ±5%
Blue, grey, black, gold
68ohms ±5%
The physical size of a resistor is indicative of the power it can dissipate.
There is an important difference between the use of three and of four bands to indicate resistance. The same resistance is encoded by:
Red, red, orange = 22 followed by 3 zeroes = 22000 (excluding default, silver, or gold tolerance)
Red, red, black, red = 220 followed by 2 zeroes = 22000 (excluding brown or other band for tolerance)
Useful mnemonics have been created to make it easier to remember the color codes. Some of these provide a hash-like mapping—a 1:1 mental or pictural translation for each color. Others just give an ordered list. Suitability of these may vary; many do not put gold (−1) and silver (−2) and especially pink (−3) in their correct numerical order, if included at all:
Betty Brown Runs Over Your Garden But Violet Gingerly Walks.
Bad Bears Raid Our Yummy Grub But Veto Grey Waffles.
BBROY from Great Britain has a Very Good Wife.
The following example includes the tolerance codes — gold, silver and none:
Bad Beer Rots Out Your Guts But Vodka Goes Well – Get Some Now.
The colors are sorted in ascending order of visible light photon frequency/energy like in a rainbow to make them easy to remember and to reduce the significance of possible read errors due to color shifts and fading over time: red (2), orange (3), yellow (4), green (5), blue (6), violet (7). Black (0) has no energy, brown (1) has a little more, white (9) has everything and grey (8) is like white, but less intense.
Capacitors
Capacitors may be marked with 4 or more colored bands or dots. The colors encode the first and second most significant digits of the value in picofarads, and the third color the decimal multiplier. Additional bands have meanings which may vary from one type to another. Low-tolerance capacitors may begin with the first 3 (rather than 2) digits of the value. It is usually, but not always, possible to work out what scheme is used by the particular colors used. Cylindrical capacitors marked with bands may look like resistors.
Extra bands on ceramic capacitors identify the voltage rating class and temperature coefficient characteristics. A broad black band was applied to some tubular paper capacitors to indicate the end that had the outer electrode; this allowed this end to be connected to chassis ground to provide some shielding against hum and noise pickup.
Postage-stamp mica capacitors marked with the EIA 3-dot and 6-dot color codes, giving capacitance value, tolerance, working voltage, and temperature characteristic. This style of capacitor was used in vacuum-tube equipment.
Capacitors of the rectangular "postage stamp" form made for military use during World War II used American War Standard (AWS) or Joint Army-Navy (JAN) coding in six dots stamped on the capacitor. An arrow on the top row of dots pointed to the right, indicating the reading order. From left to right the top dots were: either black, indicating JAN mica, or silver, indicating AWS paper; first significant digit; and second significant digit. The bottom three dots indicated temperature characteristic, tolerance, and decimal multiplier. The characteristic was black for ±1000ppm/°C, brown for ±500, red for ±200, orange for ±100, yellow for −20 to +100ppm/°C, and green for 0 to +70ppm/°C.
A similar six-dot code by EIA had the top row as first, second and third significant digits and the bottom row as voltage rating (in hundreds of volts; no color indicated 500 volts), tolerance, and multiplier. A three-dot EIA code was used for 500 volt 20% tolerance capacitors, and the dots signified first and second significant digits and the multiplier. Such capacitors were common in vacuum tube equipment and in surplus for a generation after the war but are unavailable now.
Inductors
Standards IEC60062/ EN60062 do not define a color code for inductors, but manufacturers of small inductors use the resistor color code, typically encoding inductance in microhenries. A white tolerance ring is used by TDK to indicate custom specifications.
Diodes
The part number for small JEDEC "1N"-coded diodes–in the form "1N4148"–is sometimes encoded as three or four rings in the standard color code, omitting the "1N" prefix. The 1N4148 would then be coded as yellow (4), brown (1), yellow (4), grey (8).
Wire
Transformer
Power transformers used in North American vacuum-tube equipment were often color-coded to identify the leads. Black was the primary connection, red secondary for the B+ (plate voltage), red with a yellow tracer was the center tap for the B+ full-wave rectifier winding, green or brown was the heater voltage for all tubes, yellow was the filament voltage for the rectifier tube (often a different voltage than other tube heaters). Two wires of each color were provided for each circuit, and phasing was not identified by the color code.
Audio transformers for vacuum tube equipment were coded blue for the finishing lead of the primary, red for the B+ lead of the primary, brown for a primary center tap, green for the finishing lead of the secondary, black for grid lead of the secondary, and yellow for a tapped secondary. Each lead had a different color since relative polarity or phase was more important for these transformers. Intermediate-frequency tuned transformers were coded blue and red for the primary and green and black for the secondary.
Other
Wires may be color-coded to identify their function, voltage class, polarity, phase or to identify the circuit in which they are used. The insulation of the wire may be solidly colored, or where more combinations are needed, one or two tracer stripes may be added. Some wiring color codes are set by national regulations, but often a color code is specific to a manufacturer or industry.
Building wiring under the US National Electrical Code and the Canadian Electrical Code is identified by colors to show energized, neutral, and grounding conductors, and to identify phases. Other color codes are used in the UK and other areas to identify building wiring or flexible cable wiring.
Mains electrical wiring, both in a building and on equipment, was once usually red for live, black for neutral, and green for earth, but this was changed as it was a hazard for color-blind people, who might confuse red and green; different countries use different conventions. Red and black are frequently used for positive and negative of battery or other single-voltage DC wiring.
Thermocouple wires and extension cables are identified by color code for the type of thermocouple; interchanging thermocouples with unsuitable extension wires destroys the accuracy of the measurement.
Automotive wiring is color-coded but standards vary by manufacturer; differing SAE and DIN standards exist.
Modern personal computer peripheral cables and connectors are color-coded to simplify connection of speakers, microphones, mice, keyboards and other peripherals, usually according to coloring schemes following recommendations such as PC System Design Guide, PoweredUSB, ATX, etc.
A common convention for wiring systems in industrial buildings is: black jacket – AC less than 1,000volts, blue jacket – DC or communications, orange jacket – medium voltage 2,300 or 4,160V, red jacket 13,800V or higher. Red-jacketed cable is also used for relatively low-voltage fire alarm wiring, but has a much different appearance.
Local area network cables may also have non-standardised jacket colors identifying, for example, process control network vs. office automation networks, or to identify redundant network connections, but these codes vary by organization and facility.
Electrical wiring–AC power wiring inside buildings, including standard color codes
Notes
↑Decoding keys, useful for restoration projects, are still available for some brands including FADA, Zenith, Philco and Bosch.
↑Most U.S. suppliers seem to have adopted the code by 1933; Atwater Kent was perhaps the slowest to change, possibly using "a few" proprietary ones until its closure in 1936.
↑This dating comes from the observation that the apparent earliest references to the term "RMA resistor color code" appear in periodicals dated 1931, none before the April issues, and that one mention in a July issue still calls it a "proposed standard." These are product announcements by resistor makers who would have no reason to "sit on" and delay the news of the standard's approval. An unnamed description of the code was printed in a February issue of that year; an RMA-branded color standard for the battery wires of radios is dated from at least 1927.
↑A 1961 Erie Company of the U.K. catalog shows a late usage of this style.
↑Numerous separate documents make up the EIA standard family. A list of RMA-descendent color coding standards might include EIA-RS-172-B, for carbon composition resistors with two digit bands, plus EIA-RS-344
for wirewound resistors, (Basically just saying the first band is double-width,) and EIA-RS-279 (from 1963; it is hard to find this on-line, but there is an RCA Engineering Dept. excerpt showing "grey" as 0.05% tolerance, and a 1963 journal piece showing a three-digit, "Film (EIA)" resistor whose coding and tolerances match the excerpt.) plus EIA-RS-196-A (1970; takes in the codes from RS-279 only changing "grey" to "gray") for film resistors with three digit bands. Then there is EIA-RS-198-B
for flat and tubular ceramic capacitors, EIA RS-335 for small tubular "composition" capacitors, EIA-RS-153-B for flat mica capacitors, the elusive EIA-RS-228 giving at least one of the many color marking styles of tantalum capacitors, (One reference for this is incomplete, giving a color table but no applicable picture of the marking style.) EIA-IS-48
for inductors, (as an "Interim Standard", this possibly was only in force for a limited time,) and EIA-RS-236-B of 1963 and the later JEDEC 236-C for 1N-series diodes. EIA-RS-164 or RMA REC-118 may possibly define the color code for "bumble-bee" tubular paper-dielectric capacitors; maybe someone has a copy. And somewhere there should be an obscure RMA standard, circa 1939, for the rare six-band, three-digit tubular capacitors that read from the middle-out.
↑The RKM code page lists many of these, which mostly use the number 60062, although in past years there were the British BS 1852:1975, Indian IS 8186-1976, and Japanese JIS C 5062, and for a time Germany split it into DIN 41429 for color codes, DIN 41314 for date codes, and DIN 40825 for "RKM" codes.
↑Contrary to statements seen in this space for about eight years, IEC 60062 never had recommendations for using color coding on capacitors, although national versions such as India's IS 8186-1976 (Without giving appropriate sequence diagrams or examples, however,) may have made such a suggestion.
↑A way to gauge which authority each resistor manufacturer follows is, by whether their published code-key makes the rare grey/gray tolerance band mean 0.01% as IEC 60062 defined it in 2016, or 0.05% like EIA RS-279
from 1963. Also, for the orientation clue on five-band resistors, (if not combining both indications,) do they widen the fifth band, or widen the last inter-band gap?
↑For example, industry giant Philco shows no use of standardization on its mica capacitors or "condensers" in 1937, and R.C.A. used proprietary color spot codes on many ceramic capacitors following the E12 value sequence which only came into general use post-1940.
↑These usually have three to five color bands on a glossy background, either ranging from yellow to light green, or pink, or light blue. Typical sources/data sheets may only mention a neutral yellowish green and pink. The rarer light blue ones usually distinguish themselves from similar-colored common resistors by having only four bands, of which none is a Shiny. But there may also be blue ones with five bands.
↑On the most common ones including many from China brands, often the distinguishing clues will be a background color of a shade of turquoise or bright lemon-lime, a graceful curvy profile, and a shorter, broader aspect ratio, slightly less stretched-out compared to typical resistors. But some, including recent ones, may instead sport a beige or brown background, as found on many resistors, just to make it interesting.
↑In several Panasonic product lines, a coding of two bands on the glass body, with head-end band widened, is used for voltages 10volts and up, and gives a direct two-digit voltage coding. Values under 10volts are indicated with three bands, with the first two giving Zener voltage in tenths of a volt, and the third band being a flag or dummy, always a duplicate of the second. There typically is one more band on the head-end wire lead, (rather than on the glass part,) giving a finer resolution reading of the measured Zener voltage.
↑The word "diode" is absent from the standard, as it covers semiconductor devices in general, although for transistors of other than cylindrical shape, it would give no specific guidance on how the sequence direction should be indicated.
↑The Texas Instruments 2N3708 transistor is a rare documented example of this.
↑These have four color bands including a widened, often red, fourth band, typically on a pea-soup green background. Littelfuse may still offer these by special order; the current standard product has printed markings instead.
↑The RMA and its successors generally use violet in their standards including the earliest published versions, with the exception of calling for purple on mica capacitors.
↑In typical modern practice, the lowest available exponent color is often taken as silver, whose numeric value is negative two, but some may go lower, using pink, with numeric value of negative three, or some substitute for pink. Some vintage resistors from when the lowest recognized exponent color was black/zero, may denormalize any value lower than 10 ohms. The current IEC 60062:2016, calling each digit band a "Significant Numeral" could be read as prohibiting all denormalizations, as leading zeroes are never "significant."
↑In this sorting scheme, the jars for the low-value resistors that have the rare pink exponent band also take any having one of the several substitute markings sometimes used instead of pink. (These include gray, or white, or silver plus gold bands, or empty gap.) A denormalized coding on a resistor, with one black head-end band, gets it placed one jar to the left, so singly-denormalized silvers go with the pinks also; accommodating some of the lowest known valued color-coded resistors, under 10 milliohms with two leading black bands, may require two jars to the left of pink in the three-digit row. Personal preference would dictate which of the two rows will hold any equivalent but non-color-coded resistors.
↑Applying the term "significant" here carries a risk that the reader will make a false inference that, to use the previous example, different levels of accuracy and uncertainty apply to the 56000 ohm values given by the two resistor codings. But in fact, if coded properly, these each specify that the value should be within 2% of exactly 56000 ohms, not within 2% of approximately 56000 ohms. In other words, the "56000" is not a measurement, which carries uncertainty; it is a specified exact ideal target value. Measurements, subject to uncertainty, are commonly made to test whether the part is within that tolerance range. To avoid having to get real technical and point out that along with the two or three marked significant digits, the target resistance has an infinite string of zero digits going off to the right of the decimal point, that are all significant, (so there is no difference in effective "significant figures of accuracy" between the two codings of the same exact target value,) just deleting the term "significant" can save a lot of effort. Arguably it is more complicated than this, as there are exceptions that would have to be mentioned, too. Old, circa-1940 catalogs may offer resistor values like 1250, 12500, or 125000, (then considered good, round numbers to use) with tolerance not given, for which the two-digit color coding then in use would in fact have been a two-significant-digit approximation of the part's advertised target value. A simpler reason for avoiding "significant" is that, of course, some small value resistors will have black as the first, and possibly second, bands; and leading zeroes are never "significant digits" under the conventional definition.
↑These may have something to do with why this article has twice (December 5th 2023 and March 14th 2024) been edited to give a wrong value for such a five-band example. It is however possible, to have a five-band resistor whose value does match the four-band code produced by erasing its black band, by choosing one whose first band (the hundreds place, the one that is actually added and deleted between the two codings) is the black one, such as a denormalized 0.82 ohm, 1% part, marked black-gray-red-silver-brown.
↑Even cases of 5% tolerance, three-digit resistors with a non-zero/non-black third digit are not necessarily crazy. Suppose a TV circuit designer needed a resistor that falls in the range 970 to 1090 ohms, and had a factory whose tolerance capability was 5%. A resistor marked 1030 ohms, 5% would be a sensible choice. But for any gold-band, 5% resistors found marked with values like 6190 or 5110 ohms, that would just be a case of, the manufacturer received an order for something weird, and they made what was requested.
↑One exception shows a resistor oriented vertically.
↑On a five- or six-band resistor of under 100 ohms, the tell-tale gold, silver, or pink band may be second or third from the tail end, but fourth from the head end, serving as the exponent in the value calculation. That is still on the tail-end side relative to the middle. To outrank all the width/spacing orientation clues, it just has to be somewhere other than the middle band, as sometimes seen on a resistor with a gratuitous fifth. Note that this rule is not looking for this band for what it is (exponent, tolerance or gratuitous) but for what it is not; these are the colors that cannot be digits because their numeric value is negative.
↑with its text that says, "The first band shall be the one nearest to the end of the resistor"
↑To further complicate the issue, a few published guides dating back 80-plus years have illustrations that go out of their way to make the most extreme "wrong-end" band placements, quite deceptive if viewed by the margin test, equally acceptable. However, as these would generally have had a Shiny for the tolerance band, their orientation would resolve at Step One.
↑Whether it is the end band or next one over depends on which revision of the IEC standard is being followed; they had some trouble making up their minds on whether to widen the fifth or sixth.
↑For example, some ceramic-tube older Erie U.K. types where there may be a gratuitous fifth band, originally pink, but possibly faded to white, and brown plastic bodied wirewound resistors following EIA RS-344, which may also have a gratuitous fifth band, often blue.
↑One rule is, on a five-band resistor having a black band at one end, and with a gold middle band, or, with no Shiny and also no gray, white, or pink in the middle three bands, (gray and white being possible substitutes for pink,) the black end band is the tail, either a gratuitous fifth, or maybe this is a rare Futaba 0.01% tolerance resistor. (Because black at the head would mean a low-value, denormalized marking which only makes sense with an exponent band of one of these colors; gold middle band has to be the exponent.) For a second rule, on a five-band resistor with a gold or silver middle band as its only Shiny, (indicating an exception to the four–five rule,) and a band of black, yellow, blue, or gray next to it, this color points toward the head end, as tolerance bands/band four of these colors are unknown on resistors with a gratuitous fifth. To further broaden that rule, if the possibility of a total-excursion type (from the U.K. in the 1960s) can be excluded, it can generally be assumed that the fourth band has to be brown or red.
↑And of course, values under 100 ohms typically have a Shiny as band four, so they resolve way up at step one!
↑Other random marks may be found too, such as a blue dot after second band, violet broken band after third solid band, or some text which may be a date code or an alternative temperature sensitivity indication.
123For illustration only. IEC 60062:2016 and IEC 60757:1982 do not specify or intend to specify color boundaries and properties, and colors shown here as example are applied for the purpose of consistent illustration only.
123456Before yellow and grey colored rings were assigned to tolerance values of ±0.02% and ±0.01% with IEC 60062:2016, some manufacturers used yellow and grey as substitute for gold (±5%) and silver (±10%) colored rings in high-voltage resistors to avoid metal particles in the lacquer. They still do, as of 2026; to change would mean canceling a product that buyers are happy with, and hoping no one would be worried about metal particles. Little confusion should result from continuing this; generally these are four-band, two-digit coded resistors, distinct from the three digit codings used with the new tight tolerances, although one Vishay data sheet, would suggest the "VR25" product can be ordered in E96 values, 5% tolerance, which would have a yellow fifth like a 0.02% resistor!)
123456Any temperature coefficient not assigned its own letter shall be marked "Z", and the coefficient found in other documentation.
123Before a grey colored ring was assigned to a tolerance of ±0.01% with IEC 60062:2016, some manufacturers used a grey colored ring to indicate a tolerance of ±0.05%, following EIA-RS-279 from 1963 and EIA-RS-196-A from 1970. Spec sheets of Yageo Corp. indicate this usage continues as of 2024.
↑These values repeat for every decade of magnitude: ... 0.68, 6.8, 68, 680, ... For resistors of 20% tolerance the E6 series, with six values: 10, 15, 22, 33, 47, 68, then 100, 150, ... is used; each value is approximately the previous value multiplied by 6√10. For 10% tolerance resistors the E12 series, with 12√10 as multiplier, is used; similar schemes up to E192, for 0.5% or tighter tolerance are used. The separation between the values is related to the tolerance so that adjacent values at the extremes of tolerance approximately just overlap; for example, in the E6 series 10 + 20% is 12, while 15 − 20% is also 12.
↑For example, stock numbers 603-CFR25SJT-52-8K6 for 8600 ohms 5%, 71-RL07S872GR36 for 8700 ohms 2%, and strangest of all, 594-MBE04140C5013FC1 for 501 k ohms, 1%, all from supplier Mouser Electronics.
↑The IEC specs only allow encoding this as the sixth band, or other oddball marks added to five solid bands, thus avoiding ambiguity, but parts marked as described in an old draft standard of the German DIN may have it as a fifth, final solid band on a two-digit resistor.
↑For example, stock numbers 279-YR1B12R1CC and 603-PNP300JR-73-120R or 594-NFR2500001001JA5 and 279-YR1B10R2CC from supplier Mouser Electronics.
↑as pink is not a valid tolerance band, and Shinies and pink cannot be a digit.
↑The ones with yellow and orange being the old reliability-rated carbon composition types; blue once implied a U.L. "failsafe" attribute on a wirewound resistor; meanings of the other colors on wirewound types are obscure.
↑This includes many whose three-digit interpretations fall into four full decades of values; that is, those with a fourth band of silver, gold, brown, or red, each sometimes found as tolerance colors on vintage and modern two-digit five-band specimens.
↑such as with black, on a "Futaba" 0.01% part, or yellow or orange as defined by IEC but not commonly offered except on leadless Vishay resistor types which would be resolved above as threes.
↑Blurry catalog pictures suggest the Firstohm PSR and PWR lines may have a brown gratuitous fifth also.
↑Indeed, most famous-name manufactures of these leadless resistors, other than Vishay, seem to have used this coding style, or to be currently adopting it, publishing data sheets that describe a missing-tolerance-band coding but show an older photo of a resistor with a full five-band coding in the heading.
↑White would be uncommon, as 10 gigohms and up would be a niche/specialty product, not likely to be color coded.
↑If one color gives particular difficulty due to not seeming to be the correct color for its digit, or if for example both red and green seem like they should be twos, it may help to, before reaching for the resistors, imagine the most difficult digit is painted on a big wall in its correct color.
↑Rider, John F.; Muhleman, M. L., eds. (April 1932). "Color coding"(PDF). Service - A Monthly Digest of Radio and Allied Maintenance. 1 (3). New York City, NY, USA: John F. Rider Publications, Inc.: 62. Retrieved 2019-11-15. Color coding of resistances used in receivers is not always according to the standard recommended by the RMA. Most of the manufacturers now are using this code. The following is a partial tabulation of receiver manufacturers and comments concerning their use of the body, tip and dot system. [...] (NB. Part 1/2 of a list of when each radio manufacturer first started using RMA color coded resistors.)
↑"9. RADIO MANUFACTURERS' ASSOCIATION STANDARDS". Mechanical Practice(PDF). Radio Matériel School. 1943. p.74. Archived from the original on 2025-02-25.
