Calculate mass-energy equivalence using Einstein's famous equation. Convert between mass and energy with TNT, kWh, MeV, and other unit conversions.
The E = mc² calculator computes the energy equivalent of mass using Einstein's most famous equation from special relativity. Published in 1905, this relationship reveals that mass and energy are interchangeable — a tiny amount of mass contains an enormous amount of energy because it is multiplied by the speed of light squared (c² ≈ 9 × 10¹⁶ m²/s²).
This equation explains why nuclear reactions release millions of times more energy than chemical reactions. When uranium-235 undergoes fission, about 0.1% of its mass converts to energy. In fusion, the mass deficit is even more favorable per nucleon. Even antimatter annihilation — the ultimate mass-to-energy conversion — follows E = mc² exactly, converting 100% of mass to energy.
The calculator supports multiple mass and energy units, provides comparisons in TNT tons, kilowatt-hours, MeV (for nuclear physics), and household energy equivalents. Whether you're exploring relativistic physics, comparing nuclear vs. chemical energy densities, or quantifying the energy content of matter, this tool makes the calculations instant and intuitive.
E = mc² is perhaps the most famous equation in physics, but calculating with it requires careful unit handling. This calculator makes it effortless to convert between mass and energy across many unit systems — from atomic mass units and MeV for nuclear physics to kilograms and TNT tons for explosive comparisons. It's an essential tool for physics students, nuclear engineers, and anyone curious about the energy content of matter.
E = mc² where E = energy (J), m = mass (kg), c = 299,792,458 m/s (speed of light). Conversely: m = E/c². Unit conversions: 1 kg = 8.988 × 10¹⁶ J = 21.5 megatons TNT ≈ 2.497 × 10¹⁰ kWh.
Result: 8.988 × 10¹⁶ J (21.5 megatons TNT)
One kilogram of mass, if completely converted to energy, yields E = 1 × (3 × 10⁸)² = 9 × 10¹⁶ J — equivalent to about 21.5 megatons of TNT, roughly 1,400 Hiroshima bombs.
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Yes. In nuclear reactions (fission and fusion), a small fraction of mass is converted. In particle-antiparticle annihilation, 100% of mass becomes energy. This is experimentally verified to extraordinary precision.
The speed of light is 3 × 10⁸ m/s, and squaring it gives ~9 × 10¹⁶ — an enormous amplification factor. This is why even milligrams of mass correspond to incredible amounts of energy.
Yes — a 1 kg object has rest energy of 9 × 10¹⁶ J. However, we cannot convert ordinary matter entirely to energy. Only nuclear processes convert a small fraction (~0.1% for fission).
The full relativistic energy equation is E² = (mc²)² + (pc)². E = mc² gives the rest energy only. Total energy for a moving particle includes kinetic energy: E = γmc² where γ is the Lorentz factor.
The Sun converts about 4.3 million tons of mass into energy every second via hydrogen fusion, producing 3.8 × 10²⁶ W of luminosity.
One amu equals 1/12 the mass of a carbon-12 atom, or 1.661 × 10⁻²⁷ kg. Its energy equivalent is 931.5 MeV — the standard conversion used in nuclear physics.