A megaton (abbreviation MT or Mt) is a unit of energy approximately equivalent to the energy released in the detonation of 1,000,000 tons of TNT. A kiloton is one-thousandth of a megaton. The megaton has traditionally been used to rate the energy output, and hence destructive power, of nuclear weapons. More recently, it has been used to describe the energy released in other highly destructive events, such as asteroid impacts.

A megaton is defined as:

The Little Boy weapon dropped on Hiroshima had a yield of approximately 13 kilotons. Thus, a megaton is equivalent to roughly 77 Hiroshima bombs.

The largest nuclear weapon ever detonated was the Tsar Bomba, which had a yield of 50 megatons.

See 1 E15 J for comparisons with other energies.