Mass-Energy Calculator (E=mc²)
Find the energy equivalent of a mass with E=mc².
Mass as frozen energy
Einstein’s famous equation reveals that mass is a hugely concentrated form of energy. Multiplying even a gram by the speed of light squared yields an astonishing amount of energy.
One gram of mass is equivalent to about 90 trillion joules — the energy of roughly 21 kilotons of TNT. It is the principle behind nuclear power and the Sun’s output.
Astonishing and private
The calculation runs in your browser, so nothing you enter is uploaded.
Frequently Asked Questions
What is E=mc²?
Einstein’s equation showing mass and energy are equivalent: energy equals mass times the speed of light squared.
Why is the number so huge?
Because the speed of light squared is enormous, even a tiny mass holds a vast amount of energy.
What units?
Kilograms give energy in joules; the tool also shows kilowatt-hours and TNT equivalent.
Browse the full set of free, private, in-browser tools.