# Pound (force)

Pound-force
Unit systemEnglish Engineering units, British Gravitational System
Symbollbf
Conversions
1 lbf in ...... is equal to ...
SI units   4.448222 N
CGS units   444,822.2 dyn
Absolute English System   32.17405 pdl

The pound of force or pound-force (symbol: lbf[1], sometimes lbf,[2]) is a unit of force or weight used in some systems of measurement including English Engineering units and the British Gravitational System.[3] Pound-force should not be confused with foot-pound, a unit of energy, or pound-foot, a unit of torque, that may be written as "lbf⋅ft"; nor should these be confused with pound-mass (symbol: lb), often simply called pound, which is a unit of mass.

## Definitions

The pound-force is equal to the gravitational force exerted on a mass of one avoirdupois pound on the surface of Earth. Since the 18th century, the unit has been used in low-precision measurements, for which small changes in Earth's gravity (which varies from place to place by up to half a percent) can safely be neglected.[4]

The 20th century, however, brought the need for a more precise definition. A standardized value for acceleration due to gravity was therefore needed.

### Product of avoirdupois pound and standard gravity

The pound-force is the product of one avoirdupois pound (exactly 0.45359237 kg) and the standard acceleration due to gravity, 9.80665 m/s2 (about 32.174049 ft/s2).[5][6][7]

The standard values of acceleration of the standard gravitational field (gn) and the international avoirdupois pound (lb) result in a pound-force equal to 4.4482216152605 N:[8]

{\displaystyle {\begin{aligned}1\,{\text{lbf}}&=1\,{\text{lb}}\times g_{\text{n}}\\&=1\,{\text{lb}}\times 9.80665\,{\tfrac {\text{m}}

This definition can be rephrased in terms of the slug. A slug has a mass of 32.174049 lb. A pound-force is the amount of force required to accelerate a slug at a rate of 1 ft/s2, so:

{\displaystyle {\begin{aligned}1\,{\text{lbf}}&=1\,{\text{slug}}\times 1\,{\tfrac {\text{ft}}
Other Languages
Deutsch: Pound-force
فارسی: پوند-نیرو
français: Livre-force
한국어: 파운드힘
italiano: Libbra forza
עברית: ליברת-כוח
македонски: Фунта-сила

norsk nynorsk: Poundforce
polski: Funt-siła
português: Libra (força)
Simple English: Pound-force