Wilhelm Siemens, in his inauguration speech as chairman of the British Association for the Advancement of Science (23 August 1882) first proposed the Joule as unit of heat, to be derived from the electromagnetic units Ampere and Ohm, in cgs units equivalent to 10 7 erg. The erg was adopted as its unit of energy in 1882. The cgs system had been declared official in 1881, at the first International Electrical Congress. As with every SI unit named for a person, its symbol starts with an upper case letter (J), but when written in full, it follows the rules for capitalisation of a common noun i.e., ' joule' becomes capitalised at the beginning of a sentence and in titles but is otherwise in lower case.

The joule is named after James Prescott Joule. This relationship can be used to define the watt. The work required to produce one watt of power for one second, or one watt-second (W⋅s) (compare kilowatt-hour, which is 3.6 megajoules).This relationship can be used to define the volt. The work required to move an electric charge of one coulomb through an electrical potential difference of one volt, or one coulomb-volt (C⋅V).One joule can also be defined by any of the following: J = k g ⋅ m 2 ⋅ s − 2 = N ⋅ m = P a ⋅ m 3 = W ⋅ s = C ⋅ V In terms of SI base units and in terms of SI derived units with special names, the joule is defined as It is named after the English physicist James Prescott Joule (1818–1889). It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second. It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied. The joule (pronounced / ˈ dʒ uː l/, JOOL or / ˈ dʒ aʊ l/ JOWL symbol: J) is the unit of energy in the International System of Units (SI).

For other uses, see Joule (disambiguation). This article is about the unit of energy or work.

Newton units in kg m s2