Pound-foot

pound-foot
Pound-foot and kilogram-force-metre are displayed on this torque wrench.
General information
Unit systemBritish Gravitational System, English Engineering Units
Unit ofTorque
Symbollbf⋅ft, lb-ft
Conversions
1 lbf⋅ft in ...... is equal to ...
   SI units   ≈ 1.355818 N⋅m
   Gravitational metric system   ≈ 0.1382550 kgf⋅m

A pound-foot (lb⋅ft), abbreviated from pound-force foot (lbf·ft), is a unit of torque representing one pound of force acting at a perpendicular distance of one foot from a pivot point. Conversely one foot pound-force (ft·lbf) is the moment about an axis that applies one pound-force at a radius of one foot.

Unit

The value in Système International (SI) units is given by multiplying the following exact factors:

This gives the exact conversion factor,

The name "pound-foot", intended to minimize confusion with the foot-pound as a unit of work, was apparently first proposed by British physicist Arthur Mason Worthington.

Despite this, in practice torque units are commonly called the foot-pound (denoted as either lb-ft or ft-lb) or the inch-pound (denoted as in-lb). Practitioners depend on context and the hyphenated abbreviations to know that these refer to neither energy nor moment of mass (as the symbol ft-lb rather than lbf-ft would imply).

Similarly, a pound-inch (or inch-pound) is the torque of one pound of force applied to one inch of distance from the pivot, and is equal to 1⁄12 lbf⋅ft (0.1129848 N⋅m). It is commonly used on torque wrenches and torque screwdrivers for setting specific fastener tension. An ounce-inch (or inch-ounce) is a smaller unit, equal to 1⁄16 of a pound-inch, or 0.7062 newton-centimetres (7.062 millinewton-metres).

See also

References

  1. 1 2 3 4 Butcher, Kenneth; Crown, Linda; Gentry, Elizabeth J. (May 2006), "The International System of Units (SI) – Conversion Factors for General Use" (PDF), NIST Special Publication 1038, archived (PDF) from the original on 2023-05-30
  2. ↑ Pickerill, Ken (2009). Today's Technician: Automotive Engine Performance Classroom Manual and Shop Manual (5th ed.). Cengage Learning. pp. 50–51. ISBN 978-1111782382.
  3. ↑ Worthington, Arthur Mason (1900). Dynamics of rotation: an elementary introduction to rigid dynamics (3rd ed.). Longmans, Green, and Co. p. 9.
  4. ↑ "Dial Torque Wrenches from Grainger". Grainger. 2020. In most US industrial settings, the torque ranges are given in ft-lb rather than lbf-ft.
  5. ↑ Erjavec, Jack (22 January 2010). Manual Transmissions & Transaxles: Classroom manual. Cengage Learning. p. 38. ISBN 978-1-4354-3933-7.