The **joule** (symbol: J) is the SI unit of energy, or work. It is named in honour of the physicist James Prescott Joule (1818–1889).

## Definition[]

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·m ^{2}·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**

## Conversions[]

1 joule is exactly 10^{7} erg.

1 joule is approximately equal to:

- 6.241506363 × 10
^{18}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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