Stefan-Boltzmann constant
Physico-chemicalExact
= 5.670 374 419… × 10−8 W m−2 K−4
- Value
- 5.670 374 419… × 10−8 W m−2 K−4
- Standard uncertainty
- exact
- Relative uncertainty
- exact
- Status
- Exact since the 2019 SI redefinition
- Symbol
- Source
- CODATA 2022 via NIST · NIST entry
NIST prints this exact value cut to 10 digits. ConstantID recomputes it from the defining constants: 5.670 374 419 184 429 453 970 996 731 89 × 10−8…
Use in a calculation
# Stefan-Boltzmann constant, CODATA 2022 (NIST)
sigma = 5.6703744191844294539709967318892309e-8 # W m^-2 K^-4, exact
# SciPy: scipy.constants.physical_constants['Stefan-Boltzmann constant']What it is
Gives the total power radiated per square metre by a perfect black body at temperature T: σT⁴. Doubling the temperature multiplies the radiated power by sixteen. Since 2019 it is exact, because it is built only from h, c and k.
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
- Stefan–Boltzmann law
- in terms of h, c and k
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 | 5.670 374 419… × 10−8 | exact | exact |
| 2018 | 5.670 374 419… × 10−8 | exact | +0.6 σ of 2014 |
| 2014 | 5.670 367(13) × 10−8 | 2.3 × 10−6 | −0.3 σ of 2010 |
| 2010 | 5.670 373(21) × 10−8 | 3.7 × 10−6 | −0.7 σ of 2006 |
| 2006 | 5.670 400(40) × 10−8 | 7.1 × 10−6 | +0.0 σ of 2002 |
| 2002 | 5.670 400(40) × 10−8 | 7.1 × 10−6 | +0.0 σ of 1998 |
| 1998 | 5.670 400(40) × 10−8 | 7.1 × 10−6 |
“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).