Gas density and Z factor
Density, compressibility factor Z, molar mass and normal/standard density of pure gases and gas mixtures at any pressure and temperature — with Nm³/h, kg/h and MMSCFD conversion.
Inputs
Results
Need the full version for your plant?
The Gas Properties Calculator Excel tool does everything here and more: 543 chemicals in one alphabetical list, or a mixture of up to 12: Z, density, cp with pressure correction, viscosity, conductivity, heating values and hazard data at any T and P. Print-ready report, any units, visible formulas, no macros.
Join PlantCalcKit — free
Be first to hear about new calculators, Excel tools and field guides — one short email when something new is ready. The calculators stay free with or without an account.
By joining you agree to our privacy policy. Unsubscribe or delete your details any time.
You are a PlantCalcKit member
Signed in as . We will email you when new tools and guides are ready.
How this calculator works
Density ρ = P·M / (Z·R·T), with the compressibility factor Z from the Peng–Robinson equation of state (1976) and the Péneloux volume shift, van der Waals mixing rules and zero binary interaction parameters. Critical constants and acentric factors for the 21 gases are those of the CoolProp reference library. The calculation was checked against reference (multi-parameter) equations of state for methane, natural gas, nitrogen, CO₂, hydrogen, propane, air, ammonia and ethylene: density within about 2 % up to 200 bar, and within 1.1 % for methane and natural gas up to 100 bar.
Example: a natural gas of 90 % methane, 5 % ethane, 2 % propane, 2 % nitrogen and 1 % CO₂ (17.82 kg/kmol) at 70 bar a and 15 °C has Z = 0.835 and a density of 62.4 kg/m³ — 16.5 % denser than the ideal-gas value. 10,000 Nm³/h of it is 7,978 kg/h, 8.99 MMSCFD, or 128 actual m³/h at line conditions.
Limits: gas phase only — near the critical temperature or the dew point the result is flagged. For custody transfer of natural gas use AGA 8 / ISO 20765 or GERG-2008. References: Peng and Robinson, Ind. Eng. Chem. Fundam. 15 (1976) 59; Péneloux, Rauzy and Fréze, Fluid Phase Equilibria 8 (1982) 7; Poling, Prausnitz and O'Connell, The Properties of Gases and Liquids, 5th ed.