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Foot-Pounds to Joules Converter

Enter a value and pick the conversion direction.

How it is calculated

The conversion is a single multiplication or division by a fixed factor: 1 ft·lb = 1.3558179483 J. Foot-pounds to joules: J = ft·lb × 1.3558179483. Joules to foot-pounds: ft·lb = J ÷ 1.3558179483, which is the same as multiplying by about 0.737562. The factor comes from the foot (0.3048 m) and the pound-force (using standard gravity of 9.80665 m/s²). Results are shown with six decimals. The tool also prints the factor for the chosen direction and echoes your input in the original unit. Zero and negative values are accepted. Because one foot-pound of work and one pound-foot of torque have the same size, a torque in lb·ft converts to newton-metres with the same factor, even though the tool labels the result in joules.

Worked example

A load of 150 ft·lb needs converting to joules. Multiply by the factor: 150 × 1.3558179483 = 203.372692 J. Check the other direction: 203.372692 ÷ 1.3558179483 = 150 ft·lb, which matches the start. In the opposite direction, 200 J becomes 200 ÷ 1.3558179483 = 147.512430 ft·lb. A quick mental check is that joules are always about 1.36 times the foot-pound figure.

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Common mistakes

  • Choosing the wrong direction. Converting 150 as joules when it is in foot-pounds gives 110.6 instead of 203.4, and the tool will not warn you.
  • Dividing when you should multiply. Going from ft·lb to J makes the number larger, going from J to ft·lb makes it smaller.
  • Confusing foot-pounds with pound-feet in context. They have the same numerical conversion, but energy and torque are different quantities and should not be mixed in a calculation.
  • Reading the reverse line as a second conversion. It only repeats the number you typed in its original unit, so it will always match your input.
  • Using the rounded 1.356 and carrying that through a long calculation. The tool uses the full factor with ten digits.

About this calculator

One foot-pound equals exactly 1.3558179483 joules — an exact conversion factor derived from the standard definitions of the foot (0.3048 m exactly) and the pound-force (based on standard gravity, 9.80665 m/s²), so converting in either direction is a straightforward multiplication or division by that constant.

Engineers, physics students, and firearms enthusiasts convert between the two units because foot-pounds (ft·lb) are the customary unit for torque and energy in the US and UK — used for torque-wrench settings, the muzzle energy of ammunition, and the work done by a falling weight — while joules are the SI unit used in most of the rest of the world's engineering specifications and physics coursework.

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Comments (1)

  • Editorial team

    Spec sheets for impact tools, air guns and drop tests often quote energy in joules, while American catalogues quote foot-pounds. Switching the direction to joules, 30 J comes out as 22.126864 ft·lb and 1 J as 0.737562 ft·lb. Keep this for energy only: a torque wrench rating in foot-pounds is a twist, and the same number does not convert to joules in any useful sense. Which kind of figure are you comparing?

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