The joule (symbol: J) is the SI unit of energy, or work. It is named in honour of the physicist James Prescott Joule (18181889).


The joule is a derived unit defined as the work done, or energy required, to exert a force of one newton for a distance of one metre, so the same quantity may be referred to as a newton metre or newton-metre (also with meter spelling), with the symbol N·m or N m. It can also be written as kg·m2·s−2. However, the newton metre is usually used as a measure of torque, not energy.

One joule is also:

  • the work required to move an electric charge of one coulomb through an electrical potential difference of one volt; or one coulomb volt, with the symbol C·V.
  • the work done to produce power of one watt continuously for one second; or one watt second (compare kilowatt-hour), with the symbol W·s


1 joule is exactly 107 erg.

1 joule is approximately equal to:

  • 6.241506363 × 1018 eV (electron-volts)
  • 0.239 cal (calorie) (small calories)
  • 2.390 × 10−4 Calorie or kilocalorie (food)
  • 9.48 × 10−4 BTU (British thermal unit)
  • 0.738 ft·lbf (foot pound force)
  • 23.7 ft·pdl (foot poundals)
  • 2.7778 × 10−7 kilowatt-hour
  • 2.7778 × 10−4 watt-hour
  • 9.8692 × 10−3 litre-atmosphere
  • the energy required to lift a small apple (102 g) one metre against Earth's gravity

Units defined in terms of the joule include:

  • 1 thermochemical calorie = 4.184 J (exact)
  • 1 International Table calorie = 4.1868 J (exact)
  • 1 watt-hour = 3600 J (exact)

See also[]

  • conversion of units
  • SI prefixes
  • orders of magnitude
  • orders of magnitude (energy)
  • electronvolt
  • watt-hour

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