How this calculator works
Replacing amount n by mass divided by molar mass in pV = nRT yields a density relation. Molar mass must be in kg/mol, while pressure and temperature are absolute. Pure-gas preset molecular weights are drawn from the NIST Chemistry WebBook; dry air uses the CIPM reference composition value 0.02896546 kg/mol. This model does not include humidity, condensation or real-gas compressibility.
Formula
rho = pM/(RT) = p/(Rs T); Rs = R/M.
Worked example
A custom gas with M = 0.03 kg/mol at 300 K and 83144.6261815 Pa has density 1 kg/m³. Doubling pressure at fixed temperature doubles its density to 2 kg/m³.
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Frequently asked questions
Is molar mass the same as molecule mass?
No. Molar mass is kilograms per mole; a single molecule mass is M divided by the Avogadro constant.
Can I enter gauge pressure?
Convert it to absolute pressure first by adding local atmospheric pressure.
What if Z is known?
For a real gas, density becomes pM/(ZRT). Use the compressibility calculator to evaluate the state correction.