# Pound-foot (torque)

pound-foot
Unit systemBritish Gravitational System, English Engineering Units
Unit ofTorque
Symbollbf⋅ft or 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.

The value in SI units is given by multiplying the following exact factors:

One pound (mass) = 0.45359237 kilograms
Standard gravity = 9.80665 m/s2
One foot = 0.3048 m

This gives the exact conversion factor:

One pound-foot = 1.3558179483314004 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 112 lbf⋅ft (0.1129848 N⋅m). It is commonly used on torque wrenches and torque screwdrivers for setting specific fastener tension.