Pound-foot (torque)

Not to be confused with Foot-pound (energy).

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.^[2] Conversely one foot pound-force (ft · lbf) is the moment about an axis that applies one pound-force at a radius of one foot.

pound-foot
Pound-foot and kilogram-force-metre are displayed on this torque wrench.
General information
Unit system	British Gravitational System, English Engineering Units
Unit of	Torque
Symbol	lbf⋅ft, lb-ft
Conversions
1 lbf⋅ft in ...	... is equal to ...
SI units	≈ 1.355818 N⋅m[1]
Gravitational metric system	≈ 0.1382550 kgf⋅m

Unit

The value in Système International (SI) units is given by multiplying the following exact factors:

One pound (mass) = 0.45359237 kilograms^[1]

Standard gravity = 9.80665 m/s^2[1]

One foot = 0.3048 m^[1]

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.^[3]

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).^[4][5] 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 (0.1129848 N⋅m). It is commonly used on torque wrenches and torque screwdrivers for setting specific fastener tension. An inch-ounce is a smaller unit, equal to 1⁄16 of an inch-pound.

See also

• Kilogram metre (torque) (kgf⋅m)