Specific gas constant for dry air
| Value | 287.0531 J/(kg·K) |
| Status | Fixed by a standard: ISO 2533 standard atmosphere |
| Source | U.S. Standard Atmosphere, 1976 (NOAA, NASA and US Air Force; a US federal work): R* = 8314.32 J/(kmol·K) divided by the sea-level molar mass M₀ = 28.9644 kg/kmol |
| Categories | ThermodynamicEngineering & Trade |
| Unit | Value |
|---|---|
| joule per kilogram-kelvin | 287.0531 J/(kg·K) |
| kilojoule per kilogram-kelvin | 0.2870531 kJ/(kg·K) |
| BTU per pound-Fahrenheit | 0.068561455 BTU/(lb·°F) |
| joule per kilogram-Celsius | 287.0531 J/(kg·°C) |
| foot pound-force per pound-Rankine | 53.352417 ft·lbf/(lb·°R) |
| kilojoule per kilogram-Celsius | 0.2870531 kJ/(kg·°C) |
| joule per gram-kelvin | 0.2870531 J/(g·K) |
| calorie per gram-Celsius | 0.068607337 cal/(g·°C) |
| kilocalorie per kilogram-Celsius | 0.068607337 kcal/(kg·°C) |
| BTU per pound-Rankine | 0.068561455 BTU/(lb·°R) |
Learning zone
Engineers rarely count moles of air; they weigh it. Dividing the molar gas constant by the molar mass of dry air gives a gas constant per kilogram, so the ideal gas law becomes p = ρRairT. That single line gives you air density directly: at 101.325 kPa and 20 °C, ρ = 101325/(287.05 × 293.15) = 1.204 kg/m³, the number behind every fan, duct and drag calculation.
The value quoted is the ICAO/ISO standard atmosphere's, based on a dry-air molar mass of 28.9644 g/mol. Real air is never quite this: humidity lowers density, because water vapour at 18 g/mol is lighter than the nitrogen and oxygen it displaces, so moist air has a slightly larger effective gas constant. Rising CO₂ has also nudged the molar mass upward in the fourth decimal since the standard was written.
Cite this page
formula.expert. (2026, November 8). Specific gas constant for dry air. https://formula.expert/constants/specific-gas-constant-dry-air