Gas Density Calculator
Density from molar mass, pressure and temperature.
Work out Gas Density. Density from molar mass, pressure and temperature. Written for the problem set you are stuck on.
CO₂ is 44.01, air averages 28.96, methane 16.04.
Gas density
1.9635 g/L
1.52× the density of air — sinks
Density comes straight out of the ideal gas law rearranged: ρ = PM/RT. At the same pressure and temperature every gas occupies the same molar volume, so density depends only on molar mass — which is why the answer scales exactly with M. The comparison against air is the practically useful part. Carbon dioxide is about 1.5× air and pools in low spaces, which is why CO₂ is a hazard in cellars and grain silos. Methane is 0.55× and rises. Real gases deviate from this near their boiling point or above roughly 10 atm.
How the Gas Density Calculator works
Enter a molar mass, pressure and temperature to get the gas density in g/L and kg/m³, the molar volume at those conditions, and how the gas compares to air. That last figure is the practical one — it tells you whether a gas pools at floor level or rises.
Also known as: density of a gas at stp · ideal gas density calculator · molar volume calculator · is this gas heavier than air
Frequently asked questions
How do I calculate the density of a gas?
ρ = PM/RT — pressure times molar mass, divided by the gas constant times absolute temperature. At STP that reduces to molar mass divided by 22.414 L.
Why does carbon dioxide collect at floor level?
Because at 44 g/mol it is about 1.5 times as dense as air at 29 g/mol. In cellars, wells and grain silos CO₂ can build up as an invisible layer at the bottom, which is why those spaces are gas-tested before entry.
Do all gases have the same molar volume?
Very nearly, at the same temperature and pressure — 22.414 L/mol at 0 °C and 1 atm. That is Avogadro's law, and it is why gas density depends only on molar mass.
When does this stop being accurate?
Near the boiling point, above roughly 10 atm, or for strongly associating gases. Under those conditions molecules interact enough that the ideal gas law needs a correction such as van der Waals.
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