Electron magnetic moment

$μ_{e}$ = −9.284 764 6917(29) × 10⁻²⁴ J T⁻¹

Value: −9.284 764 6917 × 10⁻²⁴ J T⁻¹
Standard uncertainty: 2.9 × 10⁻³³ J T⁻¹
Relative uncertainty: 3.1 × 10⁻¹⁰ (312 parts per trillion)
Status: Measured
Symbol: $μ_{e}$
Source: CODATA 2022 via NIST · NIST entry

Use in a calculation

# electron magnetic moment, CODATA 2022 (NIST)
electron_magnetic_moment = -9.2847646917e-24  # J T^-1, standard uncertainty 2.9e-33

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

What it is

The magnetic moment of the electron, the lightest charged particle and the carrier of electric current in metals: 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	−9.284 764 6917(29) × 10⁻²⁴	3.1 × 10⁻¹⁰	+4.5 σ of 2018
2018	−9.284 764 7043(28) × 10⁻²⁴	3.0 × 10⁻¹⁰	−1.5 σ of 2014
2014	−928.476 4620(57) × 10⁻²⁶	6.1 × 10⁻⁹	−1.5 σ of 2010
2010	−928.476 430(21) × 10⁻²⁶	2.3 × 10⁻⁸	−2.3 σ of 2006
2006	−928.476 377(23) × 10⁻²⁶	2.5 × 10⁻⁸	+0.4 σ of 2002
2002	−928.476 411(80) × 10⁻²⁶	8.6 × 10⁻⁸	−1.3 σ of 1998
1998	−928.476 362(37) × 10⁻²⁶	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).