Ideal Gas Density Calculator

How it is calculated

The tool rearranges the ideal gas law into ρ = P × M ÷ (R × T). Pressure P is entered in atmospheres (atm), molar mass M in g/mol, and temperature in degrees Celsius, which the tool converts to kelvin with T = °C + 273.15. R is the gas constant 0.0820573 L·atm/(mol·K). With these units the density comes out in g/L, which is numerically the same as kg/m³, so both are shown. Pressure may be zero or more, molar mass must be above zero, and the temperature must stay above absolute zero (−273.15 °C), otherwise there is no result. Because the ideal gas law is assumed, the answer becomes less accurate at high pressure or near the temperature where the gas turns to liquid.

Common mistakes

• Entering pressure in pascals, bar or psi. The field is in atmospheres, so 101325 would give an answer around 100,000 times too large. Convert first (1 atm = 101,325 Pa, about 1.013 bar).
• Entering the temperature in kelvin. The field expects Celsius; typing 293 would add 273.15 again and give a far too low density.
• Using the molar mass in kg/mol instead of g/mol, which shifts the answer by a factor of 1000.
• Using the atomic mass for a molecular gas, such as 16 for oxygen instead of 32 g/mol for O₂, or 14 for nitrogen instead of 28.
• Applying the result to a gas at very high pressure, or to a mixture with water vapour, without checking whether the ideal-gas assumption still holds.