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Specific Gas Constant Calculator.

Calculate a gas's specific gas constant from molar mass.

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Specific gas constant: 287.002507 J/(kg·K)

Specific gas constant

0.000000J/(kg·K)

Results update automatically as you type.

Use Cases

Engineering calculations

Use the specific gas constant in thermodynamic equations for compressible flow, gas dynamics, and HVAC system design.

Example: For air (M ≈ 0.02897 kg/mol), R_specific ≈ 287 J/(kg·K).

Physics and chemistry education

Quickly find the specific gas constant for gases in homework problems or lab reports without manual calculation.

Example: For helium (M ≈ 0.004 kg/mol), R_specific ≈ 2077 J/(kg·K).

Frequently Asked Questions

What is the specific gas constant?
The specific gas constant (R_specific) is the universal gas constant (R) divided by the molar mass (M) of the gas. It appears in the ideal gas law as p = ρ R_specific T, where ρ is density. Its value depends on the gas.
How do I use this calculator?
Enter the molar mass of the gas in kg/mol. The calculator divides the universal gas constant (8.314 J/(mol·K)) by the molar mass to give the specific gas constant in J/(kg·K).
What units should I use for molar mass?
The calculator expects molar mass in kilograms per mole (kg/mol). If you have the molar mass in g/mol, divide by 1000 before entering it.

Tips & Common Mistakes

Tips

  • Double-check the molar mass value: use the exact molar mass of the gas (e.g., for air, use 0.02897 kg/mol) for accurate results.
  • Remember that the specific gas constant is unique to each gas; it is not a universal constant.
  • If you know the gas's density and temperature, you can use the specific gas constant to find pressure via the ideal gas law.
  • For mixtures, use the average molar mass of the mixture to get an effective specific gas constant.

Common Mistakes to Avoid

  • Using molar mass in g/mol instead of kg/mol – always convert to kg/mol first.
  • Confusing the specific gas constant with the universal gas constant (R = 8.314 J/(mol·K)).
  • Forgetting that the calculator gives the specific gas constant per unit mass, not per mole.

Last updated: August 13, 2026