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 The pound of force or pound-force (symbol: lbf, sometimes lbf,) is a unit of force used in some systems of measurement, including English Engineering units and the foot–pound–second system. Pound-force should not be confused with pound-ma ...

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 made ...

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

= :

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 metre The newton-metre (also newton metre or newton meter; symbol N⋅m or N m) is the unit of torque (also called ) in the International System of Units (SI). One newton-metre is equal to the torque resulting from a force of one newton applie ...

s. The name "pound-foot", intended to minimize confusion with the

foot-pound The foot-pound force (symbol: ft⋅lbf, ft⋅lbf, or ft⋅lb ) is a unit of work or energy in the engineering and gravitational systems in United States customary and imperial units of measure. It is the energy transferred upon applying a fo ...

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 tr ...

, 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 wrench A torque wrench is a tool used to apply a specific torque to a fastener such as a nut, bolt, or lag screw. It is usually in the form of a socket wrench with an indicating scale, or an internal mechanism which will indicate (as by 'clicking', a s ...

es and

torque screwdriver A torque screwdriver is a screwdriver with components that ensure tightening to a specified torque, ensuring tightening which is sufficient, but not excessive. An insufficiently tightened screw connection may loosen in operation, and excessive ti ...

s for setting specific fastener tension.

References

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