Energy is defined via work, so the SI unit of energy is the same as the unit of work – the joule (J), named in honour of James Prescott Joule and his experiments on the mechanical equivalent of heat. In slightly more fundamental terms, 1 joule is equal to 1 newton metre and, in terms of SI base units
An energy unit that is used in atomic physics, particle physics, and high energy physics is the electronvolt (eV). One eV is equivalent to 1.602176634×10 J.