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

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 to calculate 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.

What is the specific gas constant?

The specific gas constant is defined as the ratio of molar gas constant to the molar mass of the gas and is measured in the units, J/kg∙K. The ideal gas law establishes the relation between the properties of the gas such that:

P * V = n * R * 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 Rs varies per different gases and mixtures. It can be written mathematically as:
Rs = R / M,
where M is the molar mass of the gas or mixture.

Alternatively, the specific gas constant also relates the two specific heat capacities for the mixture or gas. The specific gas constant for constant pressure Cp and for constant volume Cv can be related as:

Rs = Cp - Cv

How to calculate specific gas constant?

Follow the steps below to calculate the specific gas constant.

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

Example: Using the specific gas constant calculator.

Estimate the specific gas constant of air. Take molar mass as 28.96 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 specific gas constant of air as:
Rs = R / M = 8.314 / 0.02896 = 287.058 J/kg∙K

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 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 universal gas constant: 8.314/0.018 = 461 J/kg∙K.

Rahul Dhari
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