Use the binding energy formula to find the mass defect, total binding energy, and binding energy per nucleon of any nuclide, then see exactly where it sits on the binding-energy-per-nucleon curve relative to the iron-56 peak.
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This binding energy formula calculator takes a nuclide's mass number A and atomic number Z, looks the neutral-atom mass up in an AME2020 reference table, and works through the mass defect step by step: sum the separated protons and neutrons, subtract the actual atomic mass, then convert the missing mass to MeV with E = mc².
The result is plotted in red on the canonical binding-energy-per-nucleon curve built from 36 reference nuclides, so you can see whether your nuclide sits on the fusion side or the fission side of the iron-56 peak — and exactly how far below the peak it falls.
The binding energy formula is E_B = Δm × c², where the mass defect Δm is the difference between the summed masses of the separated nucleons and the actual mass of the atom. Using atomic masses, Δm = Z·m_H + N·m_n − M_atomic, and multiplying by 931.494 MeV/u converts the defect straight into MeV.
Mass defect is the missing mass of a nucleus: a bound nucleus always weighs less than its separated protons and neutrons. That missing mass was released as the binding energy that holds the nucleus together.
Below iron, adding nucleons increases the fraction of neighbours each nucleon can bind to, so binding energy per nucleon rises. Above iron, growing proton–proton electrostatic repulsion outweighs that gain, so the curve falls. That is why light nuclei release energy by fusion and heavy nuclei release energy by fission.
Tabulated nuclide masses are neutral-atom masses, so they already include Z electrons. Multiplying Z by the atomic mass of hydrogen-1 (which also includes one electron) makes those electron masses cancel exactly, leaving a clean nuclear result.
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