Atomic mass constant energy equivalent
| Value | 1.49241808768e-10 J |
| Status | Measured: ± 4.60e-20 J (3.1e-10 relative) |
| Source | CODATA 2022 |
| Categories | Universal & Atomicnuclearatomic |
| joule | 1.4924181e-10 J |
| kilojoule | 1.4924181e-13 kJ |
| megajoule | 1.4924181e-16 MJ |
| calorie | 3.5669648e-11 cal |
| kilocalorie | 3.5669648e-14 kcal |
| watt-hour | 4.1456058e-14 Wh |
| kilowatt-hour | 4.1456058e-17 kWh |
| British thermal unit | 1.4145394e-13 BTU |
| foot-pound | 1.1007511e-10 ft⋅lb |
| electron volt | 931,494,100 eV |
| kiloelectron volt | 931,494.1 keV |
| megaelectron volt | 931.4941 MeV |
Learning zone
931.494 MeV per atomic mass unit is the number that turns a nuclear mass table into an energy budget. Weigh the reactants and products of a nuclear reaction in daltons, take the difference, multiply by 931.494, and you have the Q-value in MeV. The mass defect of ⁴He is 0.030 377 u, so its binding energy is 28.30 MeV — 7.07 MeV per nucleon — and that is the energy the Sun harvests four hydrogen nuclei at a time.
The same factor explains why fission and fusion are worth doing at all: the binding curve peaks near ⁵⁶Fe at about 8.8 MeV per nucleon, so climbing towards iron from either end releases energy. A single U-235 fission converts roughly 0.19 u — about 180 MeV — while a chemical bond breaks for a few eV, a ratio of some 50 million. Use the conversion table on this page to read the same energy in MeV, keV or joules.