Mass-Energy Equivalence Calculator
E = mc², in joules, kWh and tonnes of TNT.
Work out Mass-Energy Equivalence. E = mc², in joules, kWh and tonnes of TNT. Written for the problem set you are stuck on.
Scientific notation works. 1 gram is 0.001 kg.
Energy equivalent
8.9876e+13 J
21,480.8 tonnes of TNT · 2.4965e+7 kWh
E = mc², for a mass converted entirely to energy. The constant is enormous — c² is about 9 × 10¹⁶ — so a single gram carries roughly 21 kilotonnes of TNT equivalent, comparable to the Hiroshima device. Nothing releases all of it. Fission converts about 0.1% of the mass and fusion about 0.7%, which is still millions of times what a chemical bond gives up. Only matter meeting antimatter converts the lot, and there is no supply of antimatter to do it with.
How the Mass-Energy Equivalence Calculator works
Enter a mass for its full energy equivalent, expressed in joules, kilowatt-hours, MeV and TNT equivalent. Nothing releases all of it — the comparison is what makes nuclear energy densities intelligible.
Also known as: e=mc2 calculator · mass to energy converter · energy of a gram of matter · einstein equation calculator
Frequently asked questions
How much energy is in a gram of matter?
About 9 × 10¹³ joules, or 21 kilotonnes of TNT equivalent — comparable to the Hiroshima device. That is the total if it were fully converted.
Does any process release all of it?
Only matter meeting antimatter, and there is no supply of antimatter to do it with. Fission converts roughly 0.1% of the mass and fusion about 0.7%.
Why is nuclear energy density so much higher than chemical?
Because chemical reactions rearrange electrons and nuclear reactions rearrange the nucleus, where binding energies are millions of times larger. The mass difference is what you are cashing in.
Does E = mc² apply to everything?
Yes — mass and energy are the same quantity. A hot object is very slightly more massive than a cold one, and a compressed spring more massive than a relaxed one. The effect is real and far too small to weigh.
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