Specific Gas Constant Calculator

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Molar mass method: divide the universal gas constant by the gas molar mass. Specific-heat method: subtract Cv from Cp. Reverse-solve: enter a known Rs to recover the molar mass.
Selecting a preset fills the molar mass automatically. Choose "Custom gas" to enter your own.
Molar mass of the gas or mixture in grams per mole. Air is about 28.97 g/mol; hydrogen is about 2.016 g/mol.
g/mol
Switch the output between SI (J/(kg·K)) and US customary / engineering (ft·lbf/(lb·R)).
Specific gas constant (Rs)
287.055

Specific gas constant for the gas or mixture

UnitJ/(kg·K)
Molar mass (M)28.9647g/mol
Rs in alt units53.1167
Specific gas constant (Rs)287.055
Molar mass (g/mol)28.9647

Specific gas constant Rs = 287.06 J/(kg·K)

  • Air has a molar mass of 28.965 g/mol, giving Rs = 287.06 J/(kg·K).
  • A higher molar mass means a smaller Rs: heavy molecules store more internal energy, so less energy goes into changing temperature per unit mass.
  • Rs relates to the universal gas constant R by Rs = R / M. It appears in the ideal gas law written per unit mass: P = ρ · Rs · T.
  • This value (287.1 J/(kg·K)) is in the range of air (287 J/(kg·K)) or nitrogen.

Next stepUse Rs in the per-mass ideal gas law P = ρ·Rs·T, or combine with the heat-capacity ratio to get Cp and Cv for compressible-flow calculations.

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