Neutron-proton mass difference energy equivalent

$(mₙ − mₚ)c²$ = 2.072 147 12(60) × 10⁻¹³ J

Value: 2.072 147 12 × 10⁻¹³ J
Standard uncertainty: 6 × 10⁻²⁰ J
Relative uncertainty: 2.9 × 10⁻⁷ (290 parts per billion)
Status: Measured
Symbol: $(mₙ − mₚ)c²$
Source: CODATA 2022 via NIST · NIST entry

Use in a calculation

# neutron-proton mass difference energy equivalent, CODATA 2022 (NIST)
neutron_proton_mass_difference_energy_eq = 2.07214712e-13  # J, standard uncertainty 6e-20

# SciPy: scipy.constants.physical_constants['neutron-proton mass difference energy equivalent']

What it is

The neutron–proton mass difference expressed as an energy, in joules.

In other units

Unit	Value
CGS (cm² g s⁻²)	2.072 147 12 × 10⁻⁶
eV electronvolt	1 293 332.51
keV kiloelectronvolt	1293.332 51
MeV megaelectronvolt	1.293 332 51
GeV gigaelectronvolt	0.001 293 332 51
Eₕ hartree	47 529.0929	unit is itself measured
Ry rydberg	95 058.1858	unit is itself measured

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	2.072 147 12(60) × 10⁻¹³	2.9 × 10⁻⁷	+0.3 σ of 2018
2018	2.072 146 89(74) × 10⁻¹³	3.6 × 10⁻⁷

“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).