The volt is defined as the potential difference across a conductor when a current of one ampere dissipates one watt of power. Hence, it is has the base SI representation m2 · kg · s-3 · A-1, which can be equally represented as one joule of energy per coulomb of charge, J/C.
Since 1990 the volt is maintained internationally using the Josephson effect, where a conventional value is used for the Josephson constant, fixed by the 18th CGPM as