Mass Defect Calculator
Enter Z, N, the proton mass, neutron mass, and nucleus mass. This calculator applies Δm = Z·mₚ + N·mₙ − mₙᵤ꜀ₗₑᵤₛ using the same selected unit for every mass.
Δm = Z·mₚ + N·mₙ − mₙᵤ꜀ₗₑᵤₛ. Use the same unit for every mass. Enter nuclear mass, not atomic mass. This tool does not assess stability or radioactivity.
Mass defect Δm:
Mass defect per nucleon:
Substituted formula:
A QUICK WALKTHROUGH
How to use this tool
- Enter the proton number Z and neutron number N.
- Choose one mass unit, then enter the proton, neutron, and nucleus masses in that unit.
- Calculate the mass defect and divide it by Z + N for the mass defect per nucleon.
Formula and source
The calculator uses Δm = Z·mₚ + N·mₙ − mₙᵤ꜀ₗₑᵤₛ, where Z and N are proton and neutron counts, and mₙᵤ꜀ₗₑᵤₛ is the mass of the nucleus. Mass defect per nucleon is Δm ÷ (Z + N). See OpenStax, University Physics Volume 3, 10.2 Nuclear Binding Energy: https://openstax.org/books/university-physics-volume-3/pages/10-2-nuclear-binding-energy .
Mass and unit requirements
Enter the proton, neutron, and nucleus masses in the same selected unit. The nucleus field requires nuclear mass, not atomic mass; atomic mass includes electrons and must not be substituted as if it were nuclear mass. This tool does not provide masses or choose a mass convention.
Calculation scope
This tool reports mass defect and mass defect per nucleon only. It does not calculate binding energy, look up isotopes, or assess nuclear stability or radioactivity. Results depend on the accuracy and convention of the values you enter.
GOOD TO KNOW
Common questions
Can I enter atomic mass in the nucleus field?
No. Enter nuclear mass for the nucleus. Atomic mass includes electrons, so it is not interchangeable with nuclear mass in this formula.
Do all three masses need the same unit?
Yes. Select one unit and enter proton, neutron, and nuclear masses in that unit.
Does a positive result mean the nucleus is stable?
No. The calculator performs arithmetic only and does not classify stability or radioactivity.