Electron volt
UnitsExact
= 1.602 176 634 × 10−19 J
- Value
- 1.602 176 634 × 10−19 J
- Standard uncertainty
- exact
- Relative uncertainty
- exact
- Status
- Exact since the 2019 SI redefinition
- Symbol
- Source
- CODATA 2022 via NIST · NIST entry
Use in a calculation
# electron volt, CODATA 2022 (NIST)
eV = 1.602176634e-19 # J, exact
# SciPy: scipy.constants.physical_constants['electron volt']What it is
The energy an electron gains when it moves through a potential difference of one volt. It is not an SI unit but is accepted for use with it; since 2019 it is exactly 1.602 176 634 × 10⁻¹⁹ joules, because e is exact.
It is built only from constants that have exact values since 20 May 2019, so it is exact too; CODATA 2018 was the first adjustment to list it that way.
Equations
- definition
In other units
| Unit | Value | |
|---|---|---|
| CGS (cm2 g s−2) | 1.602 176 634 × 10−12 | exact |
| eV electronvolt | 1 | exact |
| keV kiloelectronvolt | 0.001 | exact |
| Eₕ hartree | 0.036 749 322 18 | unit is itself measured |
| Ry rydberg | 0.073 498 644 35 | unit is itself measured |
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.
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). Diamonds mark adjustments in which the value was exact.
Relative uncertainty
| CODATA | Value (uncertainty) | Relative uncertainty | Change from previous |
|---|---|---|---|
| 2022 | 1.602 176 634 × 10−19 | exact | exact |
| 2018 | 1.602 176 634 × 10−19 | exact | +1.3 σ of 2014 |
| 2014 | 1.602 176 6208(98) × 10−19 | 6.1 × 10−9 | +1.6 σ of 2010 |
| 2010 | 1.602 176 565(35) × 10−19 | 2.2 × 10−8 | +1.9 σ of 2006 |
| 2006 | 1.602 176 487(40) × 10−19 | 2.5 × 10−8 | −0.3 σ of 2002 |
| 2002 | 1.602 176 53(14) × 10−19 | 8.7 × 10−8 | +1.1 σ of 1998 |
| 1998 | 1.602 176 462(63) × 10−19 | 3.9 × 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).