Natural unit of mass
UnitsMeasured
= 9.109 383 7139(28) × 10−31 kg
- Value
- 9.109 383 7139 × 10−31 kg
- Standard uncertainty
- 2.8 × 10−40 kg
- Relative uncertainty
- 3.1 × 10−10 (307 parts per trillion)
- Status
- Measured
- Symbol
- Source
- CODATA 2022 via NIST · NIST entry
Use in a calculation
# natural unit of mass, CODATA 2022 (NIST)
natural_unit_of_mass = 9.1093837139e-31 # kg, standard uncertainty 2.8e-40
# SciPy: scipy.constants.physical_constants['natural unit of mass']What it is
The unit of mass in the natural units of relativistic quantum mechanics, where ħ, c and the electron mass are set to 1.
In other units
| Unit | Value | |
|---|---|---|
| CGS (g) | 9.109 383 7139 × 10−28 | |
| eV/c² electronvolt / c² | 510 998.950 69 | |
| MeV/c² MeV / c² | 0.510 998 950 69 |
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 | 9.109 383 7139(28) × 10−31 | 3.1 × 10−10 | +4.4 σ of 2018 |
| 2018 | 9.109 383 7015(28) × 10−31 | 3.1 × 10−10 | +1.3 σ of 2014 |
| 2014 | 9.109 383 56(11) × 10−31 | 1.2 × 10−8 | +1.6 σ of 2010 |
| 2010 | 9.109 382 91(40) × 10−31 | 4.4 × 10−8 | +1.7 σ of 2006 |
| 2006 | 9.109 382 15(45) × 10−31 | 4.9 × 10−8 | −0.3 σ of 2002 |
| 2002 | 9.109 3826(16) × 10−31 | 1.8 × 10−7 | +1.0 σ of 1998 |
| 1998 | 9.109 381 88(72) × 10−31 | 7.9 × 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).