Engineers often write the ideal gas law per kilogram, p = ρR_sT. The specific gas constant depends on the gas: 287 J/(kg·K) for air, 4,124 for hydrogen.
How to use the Specific Gas Constant Calculator
- Method
- Gas
- Molar mass M (g/mol)
- Specific heat c_p
- Specific heat c_v
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Choose the method: from a gas preset or molar mass, or from the specific heats.
Tips
- Use absolute temperature (K) in gas laws and efficiency formulas.
- Temperature differences are the same in K and °C.
- Heat = mass × specific heat × temperature change when no phase change occurs.
- Phase changes need latent heat at a constant temperature.
Common mistakes to avoid
- Using °C in pV = nRT.
- Forgetting latent heat during melting or boiling.
- Confusing heat capacity (J/K) with specific heat (J/(kg·K)).
Inputs explained
| Field | What to enter |
|---|---|
| Method | Choose one: From molar mass, From c_p and c_v |
| Gas | Choose one: Air, Nitrogen N₂, Oxygen O₂, Hydrogen H₂ … |
| Molar mass M (g/mol) | A number |
| Specific heat c_p | Units: J/(kg·K), kJ/(kg·K), J/(g·K), BTU/(lb·°F), cal/(g·°C) |
| Specific heat c_v | Units: J/(kg·K), kJ/(kg·K), J/(g·K), BTU/(lb·°F), cal/(g·°C) |
Example values
How the main result changes when Molar mass M changes and everything else stays at the example values above:
| Molar mass M (g/mol) | Specific gas constant R_s (J/(kg·K)) |
|---|---|
| 14.48 | 287.052 |
| 21.72 | 287.052 |
| 28.97 | 287.052 |
| 36.21 | 287.052 |
| 43.45 | 287.052 |
| 57.93 | 287.052 |
Formula
R_s = R/M = c_p − c_vWorked example
Inputs — Method: From molar mass; Gas: Air.
Results — Specific gas constant R_s = 287.05205 J/(kg·K); Heat capacity ratio γ = 1.4.
Key terms
- Specific gas constant
- Gas constant per unit mass.
Frequently asked questions
What is R_s for air?
About 287.05 J/(kg·K).
How is it related to the universal gas constant?
R_s = R/M.
Why does hydrogen have a large R_s?
Its molar mass is tiny.
What is γ?
The ratio c_p/c_v (1.4 for air).
What formula does the Specific Gas Constant Calculator use?
R_s = R/M = c_p − c_v.