Ideal Gas Density

Calculate gas density from pressure and temperature using ρ = P / (R T). Select a gas preset or enter a custom specific gas constant R.

Fluid Properties & Statics

Gas — click to set R

Absolute pressure P (kPa)

Always use absolute pressure.

Temperature T (°C)

= 293.15 K

Specific gas constant R (J/(kg·K))

R = R_u / M, where R_u = 8.314 J/(mol·K) and M is molar mass in kg/mol.

Gas	Formula	M (g/mol)	R (J/kg·K)	ρ at 20°C, 1 atm (kg/m³)
Air	N₂+O₂+Ar	28.97	287.05	1.204
Nitrogen N₂	N₂	28.01	296.8	1.165
Oxygen O₂	O₂	32	259.84	1.33
CO₂	CO₂	44.01	188.92	1.83
Hydrogen H₂	H₂	2.016	4124.2	0.08381
Helium	He	4.003	2077.1	0.1664
Methane CH₄	CH₄	16.04	518.28	0.6669
Steam H₂O	H₂O	18.02	461.52	0.7489

Ideal gas law forms:

PV = nR_uT → ρ = PM / (R_u T) → ρ = P / (R T)

R = R_u / M where R_u = 8.314 J/(mol·K), M = molar mass [kg/mol]

When ideal gas law breaks down:

Near the critical point (high pressure, low temperature)
At very high pressures (P > ~10 MPa for most gases)
For polar molecules at moderate conditions (use van der Waals or Peng-Robinson)
Compressibility factor Z = PV/(nR_uT) ≈ 1 for ideal gas; use ρ = P/(ZRT) for real gas

Where: