Molar gas constant
Physico-chemicalExact
= 8.314 462 618… J mol−1 K−1
- Value
- 8.314 462 618… J mol−1 K−1
- 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: 8.314 462 618 153 24…
Use in a calculation
# molar gas constant, CODATA 2022 (NIST)
R = 8.31446261815324 # J mol^-1 K^-1, exact
# SciPy: scipy.constants.physical_constants['molar gas constant']What it is
The Boltzmann constant scaled up to a mole: the energy per kelvin per mole that appears in the ideal gas law. Since 2019 it is exact, as the product of two exact constants.
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
- ideal gas law
- definition
In other units
Gas constant R in L·atm/(mol·K), cal/(mol·K) and other units →
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 | 8.314 462 618… | exact | exact |
| 2018 | 8.314 462 618… | exact | +0.6 σ of 2014 |
| 2014 | 8.314 4598(48) | 5.8 × 10−7 | −0.3 σ of 2010 |
| 2010 | 8.314 4621(75) | 9.0 × 10−7 | −0.7 σ of 2006 |
| 2006 | 8.314 472(15) | 1.8 × 10−6 | +0.0 σ of 2002 |
| 2002 | 8.314 472(15) | 1.8 × 10−6 | +0.0 σ of 1998 |
| 1998 | 8.314 472(15) | 1.8 × 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).