**TNT equivalent** is a convention for expressing energy, typically used to describe the energy released in an explosion. The ton of TNT is a unit of energy defined by that convention to be 4.184 gigajoules,[1] which is the approximate energy released in the detonation of a metric ton (1,000 kilograms) of TNT. In other words, for each gram of TNT exploded, 4184 joules (or one large Calorie = 1,000 calories) of energy is released.

This convention intends to compare the destructiveness of an event with that of traditional explosive materials, of which TNT is a typical example, although other conventional explosives such as dynamite contain more energy.

The "**kiloton** (of TNT)" is a unit of energy equal to 4.184 terajoules (4.184×1012 J).

The "**megaton** (of TNT)" is a unit of energy equal to 4.184 petajoules (4.184×1015 J).

The kiloton and megaton of TNT have traditionally been used to describe the energy output, and hence the destructive power, of a nuclear weapon. The TNT equivalent appears in various nuclear weapon control treaties, and has been used to characterize the energy released in such other highly destructive events as an asteroid impact.[2]

Alternative values for TNT equivalency can be calculated according to which property is being compared and when in the two detonation processes the values are measured.[3][4][5][6]

Where for example the comparison is by energy yield, an explosive's energy is normally expressed for chemical purposes as the thermodynamic work produced by its detonation. For TNT this has been accurately measured as 4686 J/g from a large sample of air blast experiments, and theoretically calculated to be 4853 J/g.[7]

But, even on this basis, comparing the actual energy yields of a large nuclear device and an explosion of TNT can be slightly inaccurate. Small TNT explosions, especially in the open, don't tend to burn the carbon-particle and hydrocarbon products of the explosion. Gas-expansion and pressure-change effects tend to "freeze" the burn rapidly. A large open explosion of TNT may maintain fireball temperatures high enough so that some of those products do burn up with atmospheric oxygen.[8]

Such differences can be substantial. For safety purposes a range as wide as 2673–6702 J has been stated for a gram of TNT upon explosion.[9]

So, one can state that a nuclear bomb has a yield of 15 kt (6.3×1013 J); but an actual explosion of a 15000 ton pile of TNT may yield (for example) 8×1013 J due to additional carbon/hydrocarbon oxidation not present with small open-air charges.[8]

These complications have been sidestepped by convention. The energy liberated by one gram of TNT was arbitrarily defined as a matter of convention to be 4184 J,[10] which is exactly one kilocalorie.

A kiloton of TNT can be visualized as a cube of TNT 8.46 metres (27.8 ft) on a side.