ConstantID

Proton relative atomic mass

Atomic & nuclearMeasured

Ar(p) = 1.007 276 466 5789(83)

Value
1.007 276 466 5789
Standard uncertainty
8.3 × 10−12
Relative uncertainty
8.2 × 10−12 (8.2 parts per trillion)
Status
Measured
Symbol
Ar(p)
Source
CODATA 2022 via NIST · NIST entry

Use in a calculation

# proton relative atomic mass, CODATA 2022 (NIST)
proton_relative_atomic_mass = 1.0072764665789  # standard uncertainty 8.3e-12

# SciPy: scipy.constants.physical_constants['proton relative atomic mass']

What it is

The mass of the proton, the nucleus of the hydrogen atom, divided by the atomic mass constant (one twelfth of the mass of a carbon-12 atom). It has no 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).

proton relative atomic mass: CODATA values 1998–2022 relative to the 2022 value, in parts per trillion, with one-standard-uncertainty bars−60−40−200+20+40+60parts per trillion1998200220062010201420182022

Relative uncertainty

proton relative atomic mass: relative standard uncertainty in each CODATA adjustment, logarithmic scale10⁻¹²10⁻¹¹10⁻¹⁰1998200220062010201420182022
CODATAValue (uncertainty)Relative uncertaintyChange from previous
20221.007 276 466 5789(83)8.2 × 10−12 −0.8 σ of 2018
20181.007 276 466 621(53)5.3 × 10−11

“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).

Related constants

Atomic & nuclear e/mp Proton charge to mass quotient 9.578 833 1430(30) × 107 C kg−1 Atomic & nuclear λC,p Proton Compton wavelength 1.321 409 853 60(41) × 10−15 m Atomic & nuclear mp/me Proton–electron mass ratio 1836.152 673 426(32) Atomic & nuclear gp Proton g factor 5.585 694 6893(16) Atomic & nuclear γp Proton gyromagnetic ratio 2.675 221 8708(11) × 108 s−1 T−1 Atomic & nuclear γp/2π Proton gyromagnetic ratio in MHz/T 42.577 478 461(18) MHz T−1 Atomic & nuclear μp Proton magnetic moment 1.410 606 795 45(60) × 10−26 J T−1 Atomic & nuclear μp/μB Proton magnetic moment to Bohr magneton ratio 1.521 032 202 30(45) × 10−3