and 15 megaton Castle Bravo explosions]]TNT equivalent is a method of quantifying the energy released in explosions. The tonne of TNT is used as a unit of energy, approximately equivalent to the energy released in the detonation of this amount of TNT.The kiloton and megaton of TNT have traditionally been used to rate the energy output, and hence destructive power, of nuclear weapons (see nuclear weapon yield). This unit is written into various nuclear weapon control treaties, and gives a sense of destructiveness as compared with ordinary explosives, like TNT. More recently, it has been used to describe the energy released in other highly destructive events, such as asteroid impacts.
A gram of TNT releases 980?1100 calories upon explosion. To define the tonne of TNT, this was arbitrarily standardized to 1000 thermochemical calories = 1 gram TNT = 4184 J (exactly). NIST Guide for the Use of the International System of Units (SI): Appendix B8 - Factors for Units Listed Alphab