Electron mass in u

$m_{e}$ = 5.485 799 090 441(97) × 10⁻⁴ u

Value: 5.485 799 090 441 × 10⁻⁴ u
Standard uncertainty: 9.7 × 10⁻¹⁵ u
Relative uncertainty: 1.8 × 10⁻¹¹ (18 parts per trillion)
Status: Measured
Symbol: $m_{e}$
Source: CODATA 2022 via NIST · NIST entry

Use in a calculation

# electron mass in u, CODATA 2022 (NIST)
electron_mass_in_u = 5.485799090441e-4  # u, standard uncertainty 9.7e-15

# SciPy: scipy.constants.physical_constants['electron mass in u']

What it is

The rest mass of the electron, the lightest charged particle and the carrier of electric current in metals, in unified atomic mass units (daltons), where 1 u is one twelfth of the mass of a carbon-12 atom.

In other units

Unit	Value
CGS (g)	9.109 383 713 92 × 10⁻²⁸
eV/c² electronvolt / c²	510 998.950 693
MeV/c² MeV / c²	0.510 998 950 693

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	5.485 799 090 441(97) × 10⁻⁴	1.8 × 10⁻¹¹	−1.3 σ of 2018
2018	5.485 799 090 65(16) × 10⁻⁴	2.9 × 10⁻¹¹	−0.3 σ of 2014
2014	5.485 799 090 70(16) × 10⁻⁴	2.9 × 10⁻¹¹	−1.8 σ of 2010
2010	5.485 799 0946(22) × 10⁻⁴	4.0 × 10⁻¹⁰	+0.1 σ of 2006
2006	5.485 799 0943(23) × 10⁻⁴	4.2 × 10⁻¹⁰	−0.1 σ of 2002
2002	5.485 799 0945(24) × 10⁻⁴	4.4 × 10⁻¹⁰	−1.3 σ of 1998
1998	5.485 799 110(12) × 10⁻⁴	2.2 × 10⁻⁹

“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).