Rest energy

Rest energy (E₀) is the energy equivalent of a resting (i.e., immobile) particle. Based on relativity theory, an equivalence relation exists between mass and energy. The energy is equal to the product of mass and the square of the speed of light: E = mc² . For example, the rest energy of a proton is 938.27208943 MeV. The rest energy of a 1 g mass is about 2.5×10⁷ kWh.