Pound-foot
Unit of torque
From Wikipedia, the free encyclopedia
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/s2;[1] and
- 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, a pound-inch (or inch-pound) 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 ounce-inch (or inch-ounce) is a smaller unit, equal to 1⁄16 of a pound-inch, or 0.7062 newton-centimetres (7.062 millinewton-metres).
See also
- Kilogram metre (torque) (kgf⋅m)