# Specific Gas Constant Calculator

Created by Rahul Dhari
Reviewed by Steven Wooding
Last updated: Jan 05, 2023

The specific gas constant calculator estimates the value of the specific gas constant using two different methods. You can calculate the specific gas constant for the gas/mixture either using the molar mass of gas or using the specific heat capacity for the gas mixture.

Read on to understand the process of calculating the specific gas constant. The value of specific gas constant comes in handy in a wide range of applications such as compressible fluids, compressors, pipelines, and aerodynamics. You can also use it to calculate the density of gases, as in our ideal gas density calculator.

## What is the specific gas constant?

The specific gas constant is defined as the ratio of the molar gas constant to the molar mass of the gas and is measured in the units, $\mathrm{J/kg\cdot K}$. The ideal gas law formula (if you don't remember it, visit our ideal gas law calculator) establishes the relation between the properties of the gas such that:

$P \cdot V = n \cdot R \cdot T$

where $P$ is pressure, $V$ is volume, $n$ is number of moles, $T$ is temperature, and $R$ universal gas constant.

The specific gas constant $R_{\mathrm{s}}$ varies per different gases and mixtures. It can be written mathematically as:

$R_\mathrm{s} = \frac{R}{M}$

where $M$ is the molar mass of the gas or mixture. If you don't know how to calculate it, visit our molar mass of gas calculator.

Alternatively, the specific gas constant also relates to the two specific heat capacities for the mixture or gas. The specific gas constant for constant pressure $C_\mathrm{p}$ and for constant volume $C_\mathrm{v}$ can be related as:

$R = C_\mathrm{p} - C_\mathrm{v}$

🙋 What's specific heat again? No worries: the specific heat calculator will help you!

## How to calculate specific gas constant?

Follow the steps below to calculate the specific gas constant.

• Step 1: Select the method to calculate the specific gas constant.

• Step 2A: If you picked the molar mass method, enter the molar mass of the gas.

• Step 3A: The calculator will return the value of the specific gas constant.

Alternatively:

• Step 2B: If you picked the specific heat method, enter the specific heat capacity at constant pressure.

• Step 3B: Enter the specific heat capacity at constant volume.

• Step 4: The calculator will return the value of the specific gas constant.

## Example: Using the specific gas constant calculator

Estimate the specific gas constant of air. Take molar mass as $28.96\ \mathrm{g/mol}$.

• Step 1: Pick molar mass method from the list.
• Step 2: Enter the molar mass of the gas.
• Step 3: The calculator will return the value of the specific gas constant of air as:
$\begin{split} R_\mathrm{s} &= \frac{R}{M} =\frac{8.31446261815324}{0.02896} \\[1.5em] &= 287.058\ \mathrm{J/kg \cdot K} \end{split}$

## Specific gas constant for common gases

Gas

Molar mass [g/mol]

Specific gas constant [J/kg·K]

Air

28.9647

287

Argon

39.948

208.13

Butane

58.122

143.05

Carbon dioxide

44.01

188.92

Chlorine

70.90

117.26

Helium

4.00

2077.1

Hydrogen

2.01

4124.2

Methane

16.04

518.28

Nitrogen

28.01

296.8

Oxygen

31.99

259.84

Propane

44.09

188.56

Water vapour

18.01

461.52

## FAQ

### How do you find the specific gas constant?

To calculate the specific gas constant: Divide the universal gas constant by the molar mass of the gas.

### How are specific gas constant and specific heat related?

The specific gas constant and specific heats of gases are related as: Rs = Cp - Cv.

### What is the specific gas constant for oxygen?

The specific gas constant for oxygen is 259.84 J/kg·K. It is calculated using its molar mass 31.99 g/mol and universal gas constant: 8.314 / 0.03199 = 259.84 J/kg·K.

### What is the specific gas constant for steam?

The specific gas constant for steam is 461 J/kg·K. It is calculated using its molar mass 18.01 g/mol and the universal gas constant: 8.314/0.018 = 461 J/kg·K.

Rahul Dhari
Method
Molar mass
Universal gas constant
J·K⁻¹·mol⁻¹
Molar mass
kg
/mol
Specific gas constant
J/(kg·K)
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