Foot-pound (energy)

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Unit system English Engineering units and British Gravitational System
Unit of Energy
Symbol ft⋅lbf 
Unit conversions
1 ft⋅lbf in ... ... is equal to ...
   SI units    1.355818 J
   CGS units    13,558,180 erg

The foot-pound force (symbol: ft⋅lbf or ft⋅lb)[1] is a unit of work or energy in the Engineering and Gravitational Systems in United States customary and imperial units of measure. It is the energy transferred upon applying a force of one pound-force (lbf) through a linear displacement of one foot. The corresponding SI unit is the joule.


The foot-pound is often used to specify the muzzle energy of a bullet in small arms ballistics, particularly in the United States.

"Foot-pound" is sometimes also used as a unit of torque (see pound-foot (torque)). In the United States this unit is often used to specify, for example, the tightness of a bolt or the output of an engine. Although they are dimensionally equivalent, energy (a scalar) and torque (a vector) are distinct physical quantities. Both energy and torque can be expressed as a product of a force vector with a displacement vector (hence pounds and feet); energy is the scalar product of the two, and torque is the vector product.

Conversion to other units

Energy units

1 foot-pound is equivalent to:

  • 1.355 817 948 331 400 4 joules
  • 13558179.483314004 ergs
  • about 1.285×10−3 British thermal units
  • 0.323832 calories
  • 8.462238×10+18 eV = 8.462238 EeV = 8.462238×10+9 GeV

Power units

  • 1 watt44.25372896 ft⋅lbf/min = 0.737562149333 ft⋅lbf/s
  • 1 horsepower (mechanical) = 33,000 ft⋅lbf/min = 550 ft⋅lbf/s

See also


  1. ^ Budynas, Richard G.; Nisbett, J. Keith (2014-01-27). Mechanical Engineering Design. McGraw Hill Education. ISBN 978-0073529288. (Subscription required (help)). 
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