Classical electron radius
Atomic & nuclearMeasured
= 2.817 940 3205(13) × 10−15 m
- Value
- 2.817 940 3205 × 10−15 m
- Standard uncertainty
- 1.3 × 10−24 m
- Relative uncertainty
- 4.6 × 10−10 (461 parts per trillion)
- Status
- Measured
- Symbol
- Source
- CODATA 2022 via NIST · NIST entry
Use in a calculation
# classical electron radius, CODATA 2022 (NIST)
classical_electron_radius = 2.8179403205e-15 # m, standard uncertainty 1.3e-24
# SciPy: scipy.constants.physical_constants['classical electron radius']What it is
The radius a sphere of charge e would need for its electrostatic energy to equal the electron's rest energy (up to a factor of order one). It is not the electron's size, which is too small to measure, but it sets the scale of light scattering by free electrons.
Equations
- definition
In other units
| Unit | Value | |
|---|---|---|
| CGS (cm) | 2.817 940 3205 × 10−13 | |
| pm picometre | 0.002 817 940 3205 | |
| fm femtometre | 2.817 940 3205 |
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 | 2.817 940 3205(13) × 10−15 | 4.6 × 10−10 | −4.4 σ of 2018 |
| 2018 | 2.817 940 3262(13) × 10−15 | 4.6 × 10−10 | +1.8 σ of 2014 |
| 2014 | 2.817 940 3227(19) × 10−15 | 6.7 × 10−10 | −1.5 σ of 2010 |
| 2010 | 2.817 940 3267(27) × 10−15 | 9.6 × 10−10 | +6.4 σ of 2006 |
| 2006 | 2.817 940 2894(58) × 10−15 | 2.1 × 10−9 | −1.3 σ of 2002 |
| 2002 | 2.817 940 325(28) × 10−15 | 9.9 × 10−9 | +1.3 σ of 1998 |
| 1998 | 2.817 940 285(31) × 10−15 | 1.1 × 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).