Proton magnetic moment

$μ_{p}$ = 1.410 606 795 45(60) × 10⁻²⁶ J T⁻¹

Value: 1.410 606 795 45 × 10⁻²⁶ J T⁻¹
Standard uncertainty: 6 × 10⁻³⁶ J T⁻¹
Relative uncertainty: 4.3 × 10⁻¹⁰ (425 parts per trillion)
Status: Measured
Symbol: $μ_{p}$
Source: CODATA 2022 via NIST · NIST entry

Use in a calculation

# proton magnetic moment, CODATA 2022 (NIST)
proton_magnetic_moment = 1.41060679545e-26  # J T^-1, standard uncertainty 6e-36

# SciPy: scipy.constants.physical_constants['proton mag. mom.']

What it is

The magnetic moment of the proton, the nucleus of the hydrogen atom: how strongly it behaves like a tiny bar magnet. A negative value means it points opposite to the spin.

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	1.410 606 795 45(60) × 10⁻²⁶	4.3 × 10⁻¹⁰	−3.2 σ of 2018
2018	1.410 606 797 36(60) × 10⁻²⁶	4.3 × 10⁻¹⁰	+1.0 σ of 2014
2014	1.410 606 7873(97) × 10⁻²⁶	6.9 × 10⁻⁹	+1.3 σ of 2010
2010	1.410 606 743(33) × 10⁻²⁶	2.3 × 10⁻⁸	+2.2 σ of 2006
2006	1.410 606 662(37) × 10⁻²⁶	2.6 × 10⁻⁸	−0.4 σ of 2002
2002	1.410 606 71(12) × 10⁻²⁶	8.5 × 10⁻⁸	+1.3 σ of 1998
1998	1.410 606 633(58) × 10⁻²⁶	4.1 × 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).