Einstein's relation between rest energy E and rest mass m: E = mc², where c is the speed of light. A small mass corresponds to a huge amount of energy because c² ≈ 9 × 10¹⁶ m²/s².

What is the mass defect?

The difference between the sum of the masses of free nucleons and the mass of the assembled nucleus. The missing mass has been converted to binding energy by E = mc².

How much energy is in 1 g of mass?

E = 0.001 × (3 × 10⁸)² ≈ 9 × 10¹³ J ≈ 21 kilotonnes of TNT. This is why fission and fusion release such enormous energies even from small amounts of mass.

What is 1 atomic mass unit in energy?

1 u = 1.661 × 10⁻²⁷ kg ≈ 931.5 MeV. Nuclear binding energies are typically expressed in MeV per nucleon (about 8 MeV for stable nuclei).

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Mass-energy equivalence calculator

E = mc² in either direction. Mass to energy or energy to mass, in joules and electron-volts.

Inputs

ConvertMass m (kg)1 atomic mass unit ≈ 1.66 × 10⁻²⁷ kg

c = 2.9980e+8 m/s.

Result

Energy E

8.988e+13J

≈

5.610e+32eV

E = mc². Mass and energy are equivalent; a tiny mass corresponds to a huge amount of energy.

How this calculator works

The calculator multiplies mass by c² to get energy, or divides energy by c² to get mass, with c = 2.998 × 10⁸ m/s. Useful for binding-energy calculations: convert the mass defect into the energy released when a nucleus forms.

Common questions

What is E = mc²?: Einstein's relation between rest energy E and rest mass m: E = mc², where c is the speed of light. A small mass corresponds to a huge amount of energy because c² ≈ 9 × 10¹⁶ m²/s².
What is the mass defect?: The difference between the sum of the masses of free nucleons and the mass of the assembled nucleus. The missing mass has been converted to binding energy by E = mc².
How much energy is in 1 g of mass?: E = 0.001 × (3 × 10⁸)² ≈ 9 × 10¹³ J ≈ 21 kilotonnes of TNT. This is why fission and fusion release such enormous energies even from small amounts of mass.
What is 1 atomic mass unit in energy?: 1 u = 1.661 × 10⁻²⁷ kg ≈ 931.5 MeV. Nuclear binding energies are typically expressed in MeV per nucleon (about 8 MeV for stable nuclei).