Ideal Gas Density

Density from the ideal gas law

Replacing the amount of gas with mass divided by molar mass gives the density relation. Density is proportional to absolute pressure and molar mass, and inversely proportional to absolute temperature. Doubling the pressure of the same gas at unchanged temperature doubles its density. The calculator handles temperature and unit conversions automatically.

Example and limitations

Nitrogen with a molar mass of 28.01 g/mol has a density of about 1.25 kg/m³ at 0 °C and 101.325 kPa. If measured density is available, the second tab rearranges the same equation to find molar mass. This result alone cannot identify the gas. Molecular interactions cause real gases to deviate from the ideal model. Use real gas property data at high pressure or near condensation. A mixture's molar mass must not be averaged directly using mass fractions.

Track pressure and temperature bases together

Consider an example gas with molar mass chosen by the user as 30 g/mol. Let absolute pressure be 120 kPa and temperature be 26.85 °C. Convert temperature using 26.85 + 273.15 = 300 K, write molar mass as 0.030 kg/mol and pressure as 120000 Pa. Density is 120000 × 0.030 / (8.314462618 × 300) ≈ 1.443 kg/m³. This molar mass does not claim a tabulated property for a particular gas. In the ideal model, multiplying density by volume at the same pressure and temperature gives gas mass.

Check the measurement record to establish whether pressure is gauge or absolute. Do not enter a gauge reading directly in the absolute pressure field. Likewise, do not combine density for a cold line with volume for a hot line. Match conditions first if recorded flow has been reduced to different reference conditions. Molar mass inferred from measured density assumes the ideal model. Measurement error or real gas deviation should not automatically be interpreted as a composition change. Keep other inputs constant when comparing pressure or temperature effects. Because temperature is absolute in the model, doubling a Celsius reading does not halve density.

Frequently asked questions

How do you calculate gas density from molecular weight?

In this example, at 101.325 kPa absolute pressure and 0 °C with molar mass 28.01 g/mol, the ideal gas density is 1.25 kg/m³. Use the ideal gas relation by dividing pressure times molar mass by the gas constant and absolute temperature, checking real gas deviations separately at high pressure.

Calculate with these values