Pound-foot (torque)

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:


 * One pound (mass) = $1.356 Nm$


 * Standard gravity = 9.80665 m/s2


 * One foot = 0.3048 m

This gives the exact conversion factor:


 * One pound-foot = 1.355 817  948  331  400  4 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.

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, 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 1/12 lbf.ft. It is commonly used on torque wrenches and torque screwdrivers for setting specific fastener tension.