Speed of light in vacuum, approximately 2.998 × 10⁸ m/s.

Enter mass in kg; E will be in joules (J). You can also use grams; result is then in J for that mass in kg.

What does E = mc² mean?

Energy and mass are equivalent; a mass m has rest energy E = mc².

Online E = mc² Calculator

Calculate mass-energy equivalence: E = mc². Enter mass to get energy (c = speed of light).

Mass m (kg)

What is c?: Speed of light in vacuum, approximately 2.998 × 10⁸ m/s.
What units for mass?: Enter mass in kg; E will be in joules (J). You can also use grams; result is then in J for that mass in kg.
What does E = mc² mean?: Energy and mass are equivalent; a mass m has rest energy E = mc².

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