Nuclear Binding Energy Calculator
Mass defect and binding energy per nucleon, from atomic mass.
Work out Nuclear Binding Energy. Mass defect and binding energy per nucleon, from atomic mass. Free, with no account and nothing to download.
The atomic mass including electrons, as tabulated — not the nuclear mass. Iron-56 is 55.934936 u.
Binding energy per nucleon
8.79 MeV
492.26 MeV total across 56 nucleons
Binding energy per nucleon peaks near iron-56 at about 8.79 MeV. Everything lighter releases energy by fusing towards it, everything heavier by fissioning towards it — which is why stars fuse up to iron and stop, and why uranium fissions. The calculation uses the hydrogen atom mass rather than the bare proton, so the Z electrons on both sides cancel and you can use tabulated atomic masses directly, which is what tables actually publish.
How the Nuclear Binding Energy Calculator works
Enter a nuclide's protons, neutrons and tabulated atomic mass to get the mass defect and the binding energy, both in total and per nucleon. The calculation uses the hydrogen atom mass rather than the bare proton, so the electrons cancel and you can use published atomic masses directly.
Also known as: mass defect calculator · binding energy per nucleon calculator · e=mc2 calculator · nuclear mass defect
Frequently asked questions
What is mass defect?
A nucleus weighs less than its separated protons and neutrons added up. That missing mass was converted to energy when the nucleus formed, and E = mc² converts it back — one atomic mass unit is 931.494 MeV.
Which nucleus has the highest binding energy per nucleon?
Nickel-62 has the highest at about 8.79 MeV, with iron-56 essentially tied. This is the peak of the binding energy curve, which is why fusion releases energy below it and fission releases energy above it.
Should I use atomic mass or nuclear mass?
Atomic mass, and this page is built for it. Because the Z electrons in the atomic mass are matched by the Z electrons in Z hydrogen atoms, they cancel exactly. Mixing a nuclear mass with hydrogen atom masses gives an answer wrong by the electron masses.
Why does fusion release more energy than fission per kilogram?
Because the binding energy curve rises far more steeply on the light side. Fusing hydrogen to helium climbs about 7 MeV per nucleon; fissioning uranium climbs under 1 MeV per nucleon.
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