Neutron-proton mass difference = 2.305 574 61 × 10−30 kg
- Value
- 2.305 574 61 × 10−30
- Unit
- kg
- Uncertainty
- 0.000 000 67 × 10⁻³⁰
- Copy-ready
2.30557461e-30
How much heavier the neutron is than the proton.
The reason a free neutron decays into a proton, an electron and an antineutrino, and why hydrogen is stable.
The same quantity, other ways NIST lists it
| Quantity (NIST name) | Value | Unit | Uncertainty |
|---|---|---|---|
| Neutron-proton mass difference energy equivalent | 2.072 147 12 × 10−13 | J | 0.000 000 60 × 10⁻¹³ |
| Neutron-proton mass difference energy equivalent in MeV | 1.293 332 51 | MeV | 0.000 000 38 |
| Neutron-proton mass difference in u | 1.388 449 48 × 10−3 | u | 0.000 000 40 × 10⁻³ |
NIST, Fundamental Physical Constants — Complete Listing (2022 CODATA adjustment), retrieved 2026-07-26.
Electrical, thermal and X-ray constants
Angstrom starConductance quantumCopper x unitElectron charge to mass quotientFermi coupling constantFirst radiation constantHartree energyJosephson constantLattice parameter of siliconLattice spacing of ideal Si (220)Loschmidt constant (273.15 K, 101.325 kPa)Magnetic flux quantumMolar mass constantMolar mass of carbon-12Molar Planck constantMolar volume of siliconMolybdenum x unitNeutron-proton mass differenceProton charge to mass quotientQuantum of circulationSackur-Tetrode constant (1 K, 101.325 kPa)Second radiation constantVon Klitzing constantWeak mixing angleWien frequency displacement law constantW to Z mass ratio