The amount of energy gained by an electron accelerated in a vacuum by a voltage of one Volt. This unit is used to express the energy of subatomic particles. It is a very small unit; by comparison, the energy of a flying mosquito is about a trillion electron volts. One electron volt is equivalent to 1.6 × 10⁻¹⁹ Joules.

The fission of a single uranium 235 nucleus releases 200 MeV of energy.

In thermonuclear fusion, the fusion of a deuterium nucleus with a tritium nucleus releases 17.53 MeV of energy.