E = mc² Calculator
Calculate rest energy from mass with the exact vacuum speed of light.
Formula
E₀ = mc²; c = 299792458 m/s
Rest mass: 1 kg · Rest energy ≈ (1 kg)×299792458^2
How to use
- Enter a nonnegative rest mass.
- Choose the mass unit.
- Read rest energy in joules.
Examples
- 1 g corresponds to about 8.99 × 10¹³ J of rest energy.
Frequently asked questions
Is this kinetic energy?
No. It is rest energy, independent of the object’s speed.
What value of c is used?
299,792,458 m/s, the exact SI value in vacuum.
Is all this energy available as fuel?
No. A process releases energy according to its mass difference and other constraints.
Sources
Updated: