Individual gas constants for common gases at standard conditions
Gas	Formula	Molecular Weight(g/mol)	R(J/(kg·K))	R(kJ/(kg·K))	R(Wh/(kg·K))	R(Btu/(lb·°F))	R(ft·lbf/(lb·°R))
Acetylene	C₂H₂	26.038	319.32	0.3193	0.0887	0.07627	59.35
Air	Mixture	28.965	287.05	0.2871	0.07974	0.06856	53.353
Ammonia	NH₃	17.031	488.21	0.4882	0.13561	0.11661	90.74
Argon	Ar	39.948	208.13	0.2081	0.05781	0.04971	38.684
Butane	C₄H₁₀	58.122	143.05	0.1431	0.03974	0.03417	26.588
Carbon Dioxide	CO₂	44.01	188.92	0.1889	0.05248	0.04512	35.114
Carbon Monoxide	CO	28.01	296.84	0.2968	0.08246	0.0709	55.171
Chlorine	Cl₂	70.906	117.26	0.1173	0.03257	0.02801	21.794
Ethane	C₂H₆	30.069	276.51	0.2765	0.07681	0.06604	51.393
Ethene	C₂H₄	28.053	296.38	0.2964	0.08233	0.07079	55.086
Fluorine	F₂	37.997	218.82	0.2188	0.06078	0.05226	40.67
Helium	He	4.003	2077.1	2.0771	0.57696	0.4961	386.047
Hydrogen	H₂	2.016	4124.2	4.1242	1.14563	0.98506	766.541
Hydrogen Chloride	HCl	36.461	228.04	0.228	0.06334	0.05447	42.384
Hydrogen Sulfide	H₂S	34.081	243.96	0.244	0.06777	0.05827	45.344
Krypton	Kr	83.798	99.22	0.0992	0.02756	0.0237	18.441
Methane	CH₄	16.042	518.28	0.5183	0.14397	0.12379	96.329
Neon	Ne	20.18	412.02	0.412	0.11445	0.09841	76.579
Nitrogen	N₂	28.013	296.8	0.2968	0.08245	0.07089	55.165
Nitrogen Dioxide	NO₂	46.006	180.73	0.1807	0.0502	0.04317	33.59
Nitrous Oxide	N₂O	44.012	188.91	0.1889	0.05248	0.04512	35.112
Oxygen	O₂	31.999	259.84	0.2598	0.07218	0.06206	48.294
Propane	C₃H₈	44.096	188.56	0.1886	0.05238	0.04504	35.045
Propene	C₃H₆	42.08	197.59	0.1976	0.05489	0.04719	36.724
Sulfur Dioxide	SO₂	64.064	129.78	0.1298	0.03605	0.031	24.122
Sulfur Hexafluoride	SF₆	146.055	56.93	0.0569	0.01581	0.0136	10.581
Water Vapor	H₂O	18.015	461.52	0.4615	0.1282	0.11023	85.78
Xenon	Xe	131.293	63.33	0.0633	0.01759	0.01513	11.77

Source: engineeringtoolbox.com

Universal Gas Constant in Alternative Units

Unit System	Value
$R_u$ in J/(mol·K)	8.3144598
$R_u$ in kJ/(kmol·K)	8.3144598
$R_u$ in atm·L/(mol·K)	0.08206
$R_u$ in bar·L/(mol·K)	0.08314
$R_u$ in cal/(mol·K)	1.9872
$R_u$ in Btu/(lbmol·°R)	1.9872
$R_u$ in lbf·ft/(lbmol·°R)	1545.349
$R_u$ in atm·ft³/(lbmol·°R)	0.73024
$R_u$ in kPa·cm³/(mol·K)	8314.46
$R_u$ in hp·h/(lbmol·°R)	0.0007805
$R_u$ in kWh/(lbmol·°R)	0.000582

Molecular Weight of a Gas Mixture

The average molecular weight of a gas mixture is calculated from the mole fractions and molecular weights of the constituent gases:

$M_{\text{mixture}} = \sum_{i=1}^{n} x_i M_i = x_1 M_1 + x_2 M_2 + \cdots + x_n M_n$

Where:

$x_i$ = mole fraction of gas $i$ in the mixture
$M_i$ = molecular weight of gas $i$

Note: For dry air, the mixture molecular weight is approximately 28.965 g/mol (28.965 kg/kmol).

Individual Universal Gas Constant

Overview

Key Formulas

Ideal Gas Law

Boyle's Law

Charles's Law

Variables

Individual Gas Constants Table

Universal Gas Constant in Alternative Units

Molecular Weight of a Gas Mixture

Interactive Charts

Air - Molecular Weight and Composition

References