Gas Mixture Density Calculator
Calculate the density of a two-component gas mixture from its composition, pressure and temperature.
How it works
M_avg = x₁·M₁ + x₂·M₂ · ρ = (P · M_avg) / (R · T), R = 0.08206 L·atm·mol⁻¹·K⁻¹
A gas mixture behaves like a single ideal gas with an average molar mass equal to the mole-fraction-weighted sum of its components. Substituting that average into the ideal-gas density expression ρ = PM/RT gives the mixture density. With pressure in atmospheres, temperature in kelvin and molar mass in g/mol, the result comes out in grams per litre.
Worked example
For a 78 % N₂ (28 g/mol) and 22 % O₂ (32 g/mol) mixture at 1 atm and 273.15 K: M_avg = 0.78×28 + 0.22×32 = 28.88 g/mol, so ρ = (1 × 28.88) / (0.08206 × 273.15) ≈ 1.289 g/L — close to real air.
Sources: Density — ideal gas — Wikipedia
Frequently asked questions
Why use an average molar mass?
By Amagat's and Dalton's laws, an ideal mixture acts as one gas whose effective molar mass is the mole-fraction-weighted average of the components. That single value plugs straight into the density formula.
Must temperature be in kelvin?
Yes. The ideal-gas law only works on the absolute (kelvin) scale, so convert Celsius by adding 273.15 before entering it.
How accurate is this for real gases?
It is very good at ordinary pressures and temperatures. Near high pressure or the condensation point, real-gas deviations make the ideal-gas density an approximation.
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