Particle Rest Energy Calculator

Summary

Enter a mass in kg, atomic mass units, or eV/c² — or pick a common particle — to get rest energy in J, eV, MeV, and GeV.

How it works

1. Select a common particle from the preset menu, or choose "Custom" to enter a mass manually.
2. Pick the input unit: kg, atomic mass units (u), or eV/c².
3. Enter the mass value in the input field.
4. The calculator applies E₀ = mc² using c = 2.99792458 × 10⁸ m/s.
5. Results are displayed in joules, eV, MeV, and GeV instantly.
6. Use the copy button next to any result to copy it to the clipboard.

Use cases

• Verify textbook E=mc² problems for electrons and protons.
• Convert particle masses between kg, u, and eV/c².
• Compare rest energies of fundamental particles side by side.
• Estimate annihilation photon energies (each photon carries E₀ of the particle).
• Cross-reference particle data with PDG values in consistent units.
• Understand why a proton’s rest energy (938 MeV) vastly exceeds an electron’s (0.511 MeV).

Frequently Asked Questions