Physics scale calculator

How much energy is in U-235 fission?

This idealized calculation uses atoms × approximately 200 MeV per fission, then applies an editable fissioned fraction and thermal-to-electric efficiency. It is not a reactor fuel-burnup model.

U-235 mass (kg)

Fraction of entered U-235 that fissions (%)

Thermal-to-electric efficiency (%)

Idealized thermal energy—

After entered efficiency—

Electrical TWh—

This is deliberately not a “1 kg of reactor fuel” calculator. Commercial fuel is not pure U-235, not all atoms fission, fuel management is complex and breeding/conversion can matter in some reactor types.