Individual & Universal Gas Constants: Definitions, Values, and Applications

Calculator and reference tool for individual and universal gas constants. Calculate individual gas constant from universal constant and molecular weight, or look up values for common gases in multiple unit systems.

Individual Gas Constant Calculator

Calculate the individual gas constant from the universal gas constant and molecular weight using the formula:

R = Ru / Mgas

where:

R = Individual Gas Constant
Ru = Universal Gas Constant
Mgas = Molecular Weight of the gas

Calculator

Inputs

Universal Gas Constant (Ru) (J/(mol·K))

Molecular Weight (Mgas) (g/mol)

Results

Individual Gas Constant (R)-- J/(kg·K)

Individual Gas Constant (R)-- ft·lbf/slug·°R

Universal Gas Constant Values

The universal gas constant (Ru) in common units:

J/(mol·K): 8.3144598
kJ/(kmol·K): 8.3144598
J/(kmol·K): 8314.472
atm·L/(mol·K): 0.082057338
cal/(mol·K): 1.9872
Btu/(lbmol·°R): 1.9872036
lbf·ft/(lbmol·°R): 1545.349
psi·ft³/(lbmol·°R): 10.73

The universal gas constant is the same for all ideal or perfect gases.

Gas	Formula	Molecular Weight (g/mol)	R (J/kg·K)	R (ft·lbf/slug·°R)
Acetylene	C₂H₂	26.038	319.32	1910
Air	Mixture	28.9647	287.05	1717
Ammonia	NH₃	17.031	488.21	2919
Argon	Ar	39.948	208.13	1245
Butane	C₄H₁₀	58.122	143.05	855
Butene	C₄H₈	56.106	148.19	886
Carbon Dioxide	CO₂	44.010	188.92	1130
Carbon Monoxide	CO	28.010	296.84	1775
Ethane	C₂H₆	30.069	276.51	1654
Ethene	C₂H₄	28.053	296.38	1772
Helium	He	4.003	2077.1	12421
Hydrogen	H₂	2.016	4124.2	24663
Hydrogen Sulfide	H₂S	34.081	243.96	1459
Methane	CH₄	16.042	518.28	3099
Nitrogen	N₂	28.013	296.80	1775
Oxygen	O₂	31.999	259.84	1554
Propane	C₃H₈	44.096	188.56	1128
Water Vapor	H₂O	18.015	461.52	2760

Key Relationships

Individual Gas Constant (R):

R = Ru / Mgas
Depends on the particular gas
Independent of temperature
Common units: J/(kg·K) or ft·lbf/slug·°R

Universal Gas Constant (Ru):

Ru = Mgas × R
The same for all ideal or perfect gases
Can be expressed as: Ru = k × NA
- k (Boltzmann's constant) = 1.381×10⁻²³ J/K
- NA (Avogadro's number) = 6.022×10²³ 1/mol

Gas Mixture Molecular Weight:

Mmixture = Σ(xi × Mi)
Average based on mole fractions of each component gas