A pound-foot (lbf⋅ft) is a unit of

torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...

representing one pound of force acting at a perpendicular distance of one

foot The foot ( : feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg mad ...

from a pivot point. Conversely one pound-foot is the

moment Moment or Moments may refer to: * Present time Music * The Moments, American R&B vocal group Albums * ''Moment'' (Dark Tranquillity album), 2020 * ''Moment'' (Speed album), 1998 * ''Moments'' (Darude album) * ''Moments'' (Christine Guldbrand ...

about an axis that applies one pound-force at a radius of one foot. The value in SI units is given by multiplying the following exact factors: :One

pound (mass) The pound or pound-mass is a unit of mass used in British imperial and United States customary systems of measurement. Various definitions have been used; the most common today is the international avoirdupois pound, which is legally defi ...

= :

Standard gravity The standard acceleration due to gravity (or standard acceleration of free fall), sometimes abbreviated as standard gravity, usually denoted by or , is the nominal gravitational acceleration of an object in a vacuum near the surface of the Earth. ...

= 9.80665 m/s² :One

= 0.3048 m This gives the exact conversion factor: :One pound-foot = newton metres. The name "pound-foot", intended to minimize confusion with the foot-pound as a unit of

work Work may refer to: * Work (human activity), intentional activity people perform to support themselves, others, or the community ** Manual labour, physical work done by humans ** House work, housework, or homemaking ** Working animal, an animal t ...

, was apparently first proposed by British physicist

Arthur Mason Worthington Arthur Mason Worthington (11 June 1852 in Manchester – 5 December 1916 in Oxford) was an English physicist and educator. He is best known for his work on fluid mechanics, especially the physics of splashes; for observing those, he pioneered t ...

. 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). In most US industrial settings, the torque ranges are given in ft-lb rather than lbf-ft. 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, an inch-pound (or ''pound-inch'') is the torque of one pound of force applied to one inch of distance from the pivot, and is equal to . It is commonly used on torque wrenches and torque screwdrivers for setting specific fastener tension.

References

Units of torque Imperial units Customary units of measurement in the United States {{Engineering-stub de:Foot-pound