| pound-foot | |
| Standard: | British Gravitational System, English Engineering Units |
| Quantity: | Torque |
| Symbol: | lbf⋅ft |
| Symbol2: | lb-ft |
| Units1: | SI units |
| Inunits1: | ≈ |
| Units2: | Gravitational metric system |
| Inunits2: | ≈ 1disp=outNaNdisp=out |
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.[1] Conversely one foot pound-force (ft · lbf) is the moment about an axis that applies one pound-force at a radius of one foot.
The value in Système International (SI) units is given by multiplying the following exact factors:
One pound (mass) =
Standard gravity = 9.80665 m/s2
One foot = 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, was apparently first proposed by British physicist Arthur Mason Worthington.[2]
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).[3] [4] 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.