ConstantID

Electron relative atomic mass

Atomic & nuclearMeasured

Ar(e) = 5.485 799 090 441(97) × 10−4

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

Use in a calculation

# electron relative atomic mass, CODATA 2022 (NIST)
electron_relative_atomic_mass = 5.485799090441e-4  # standard uncertainty 9.7e-15

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

What it is

The mass of the electron, the lightest charged particle and the carrier of electric current in metals, 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).

electron 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

electron relative atomic mass: relative standard uncertainty in each CODATA adjustment, logarithmic scale10⁻¹²10⁻¹¹10⁻¹⁰1998200220062010201420182022
CODATAValue (uncertainty)Relative uncertaintyChange from previous
20225.485 799 090 441(97) × 10−41.8 × 10−11 −1.3 σ of 2018
20185.485 799 090 65(16) × 10−42.9 × 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/me Electron charge to mass quotient −1.758 820 008 38(55) × 1011 C kg−1 Atomic & nuclear μe/μd Electron-deuteron magnetic moment ratio −2143.923 4921(56) Atomic & nuclear me/md Electron-deuteron mass ratio 2.724 437 107 629(47) × 10−4 Atomic & nuclear ge Electron g-factor −2.002 319 304 360 92(36) Atomic & nuclear γe Electron gyromagnetic ratio 1.760 859 627 84(55) × 1011 s−1 T−1 Atomic & nuclear γe/2π Electron gyromagnetic ratio in MHz/T 28 024.951 3861(87) MHz T−1 Atomic & nuclear me/mh Electron-helion mass ratio 1.819 543 074 649(53) × 10−4 Atomic & nuclear μe Electron magnetic moment −9.284 764 6917(29) × 10−24 J T−1