# Specific Gas Constant Calculator

URL: https://speedycalculator.com/calculators/physics/specific-gas-constant/
Last updated: 2026-10-30

> The specific gas constant calculator finds R_s of a gas from its molar mass or from its specific heats c_p and c_v, with values for common gases.

## Inputs

- Method
- Gas
- Molar mass M (g/mol)
- Specific heat c_p (J/(kg·K), kJ/(kg·K), J/(g·K), BTU/(lb·°F), cal/(g·°C))
- Specific heat c_v (J/(kg·K), kJ/(kg·K), J/(g·K), BTU/(lb·°F), cal/(g·°C))

## Results

- Specific gas constant R_s
- Heat capacity ratio γ

## Formula

```
R_s = R/M = c_p − c_v
```

## Explanation

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

FieldWhat to enterMethodChoose one: From molar mass, From c_p and c_vGasChoose one: Air, Nitrogen N₂, Oxygen O₂, Hydrogen H₂ …Molar mass M (g/mol)A numberSpecific heat c_pUnits: J/(kg·K), kJ/(kg·K), J/(g·K), BTU/(lb·°F), cal/(g·°C)Specific heat c_vUnits: 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))14.48287.05221.72287.05228.97287.05236.21287.05243.45287.05257.93287.052

## Worked 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.

## FAQ

**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.


## Sources

- [NIST – Fundamental physical constants](https://physics.nist.gov/cuu/Constants/)
- [OpenStax – University Physics Volume 2](https://openstax.org/details/books/university-physics-volume-2)
- [HyperPhysics (Georgia State University)](http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html)