Proton mass energy equivalent in MeV

$m_{p} c^{2}$ = 938.272 089 43(29) MeV

Value: 938.272 089 43 MeV
Standard uncertainty: 2.9 × 10⁻⁷ MeV
Relative uncertainty: 3.1 × 10⁻¹⁰ (309 parts per trillion)
Status: Measured
Symbol: $m_{p} c^{2}$
Source: CODATA 2022 via NIST · NIST entry

Use in a calculation

# proton mass energy equivalent in MeV, CODATA 2022 (NIST)
proton_mass_energy_equivalent_in_mev = 9.3827208943e2  # MeV, standard uncertainty 2.9e-7

# SciPy: scipy.constants.physical_constants['proton mass energy equivalent in MeV']

What it is

The rest energy (mass × c²) of the proton, the nucleus of the hydrogen atom, in mega-electronvolts, the unit particle physicists use.

In other units

Unit	Value
CGS (cm² g s⁻²)	0.001 503 277 618
keV kiloelectronvolt	938 272.089 43
GeV gigaelectronvolt	0.938 272 089 43
erg erg	0.001 503 277 618

Converted with ConstantID's unit table; digits are rounded to the precision of the value, and a long exact value is rounded only for display. The relative uncertainty is unchanged by conversion to an exactly defined unit.

How the value changed, 1998–2022

Each point is one CODATA adjustment, plotted as its difference from the 2022 value; the bars show one standard uncertainty (an arrowhead means the bar runs off the chart).

Relative uncertainty

CODATA	Value (uncertainty)	Relative uncertainty	Change from previous
2022	938.272 089 43(29)	3.1 × 10⁻¹⁰	+4.4 σ of 2018
2018	938.272 088 16(29)	3.1 × 10⁻¹⁰	+1.2 σ of 2014
2014	938.272 0813(58)	6.2 × 10⁻⁹	+1.7 σ of 2010
2010	938.272 046(21)	2.2 × 10⁻⁸	+1.4 σ of 2006
2006	938.272 013(23)	2.5 × 10⁻⁸	−0.2 σ of 2002
2002	938.272 028(80)	8.5 × 10⁻⁸	+0.8 σ of 1998
1998	938.271 998(38)	4.0 × 10⁻⁸

“Change from previous” is the shift in the value divided by the standard uncertainty of the previous adjustment. Earlier values are converted into the current unit where NIST changed it (for example J s to J Hz⁻¹).