Mass-Energy Equivalence Calculator (E = mc²)
Einstein's famous equation E = mc² reveals that mass and energy are interchangeable. A small amount of mass contains an enormous amount of energy because the speed of light squared (c² ≈ 9 × 10¹⁶ m²/s²) is such a large number. This calculator converts between mass and energy in both directions, with results in Joules, MeV, and TNT equivalent.
The mass-energy equivalence E = mc², published by Albert Einstein in 1905 as part of special relativity, shows that mass itself is a form of energy. The speed of light c = 299,792,458 m/s is so large that even tiny amounts of mass correspond to enormous energies.
For example, 1 kilogram of matter fully converted to energy yields about 9 × 10¹⁶ Joules, equivalent to roughly 21.5 megatons of TNT. This is the energy released by a large thermonuclear weapon. In nuclear fission, only about 0.1% of mass is converted; in fusion, about 0.7%. Even these tiny fractions release tremendous energy.
The equation works in reverse too: energy has an equivalent mass. The heat added to a pot of boiling water increases its mass by an immeasurably small amount. At the subatomic scale, the mass of a proton is mostly binding energy of quarks rather than the rest mass of the quarks themselves. E = mc² is not just a theoretical curiosity but the foundation of nuclear power, particle physics, and cosmology.