E = mc² Calculator

E = mc² Formula

Worked Example

Converting 1 gram of mass entirely into energy:

1. E = m × c²
2. E = 0.001 × c²
3. E = 89875517870000 J

In MJ: 89875517.87 MJ · In cal: 21480764310000 cal · In kcal: 21480764310 kcal · In Wh: 24965421630 Wh · TNT equivalent (1 t TNT = 4.184 GJ): 21480.76431 t TNT · In MeV: 5.609588604 × 10²⁶ MeV · c (exact): 299,792,458 m/s

Atomic mass unit

One unified atomic mass unit (1 u = 1.66054 × 10⁻²⁷ kg) is equivalent to 931.494 MeV, the conversion nuclear physicists use for reaction energies.

More Modern Physics Calculators

• Photon Energy Calculator

  E = h f = h c / λ

  h = 6.62607015 × 10⁻³⁴ J·s, c = 299,792,458 m/s (both exact), f frequency, λ wavelength

  Example: A photon of green light with a wavelength of 500 nm: Photon energy E = 2.47968 eV.

  Open the photon energy calculator →

• Half-Life Calculator

  N = N₀ (½)^(t / T½)

  N amount left, N₀ initial amount, t elapsed time, T½ half-life; λ = ln 2 / T½

  Example: 100 g of carbon-14 (half-life 5730 years) after 11,460 years: Amount remaining N = 25.

  Open the half-life calculator →

• de Broglie Wavelength Calculator

  λ = h / p = h / (m v) = h / √(2 m K)

  h Planck constant, p momentum, m mass, v speed, K kinetic energy (= qV after acceleration through V volts)

  Example: An electron accelerated from rest through 100 V: de Broglie wavelength λ = 0.122643 nm.

  Open the de broglie wavelength calculator →

Frequently asked questions

Sources

• CODATA Recommended Values of the Fundamental Physical Constants: 2018, National Institute of Standards and Technology .

Last reviewed: 2026-10-15. Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.