Molar Volume Calculator

Molar volume is the volume occupied by one mole of a substance. For an ideal gas it equals the gas constant times temperature divided by pressure (Vm = RT/P). At standard temperature and pressure of 0 degrees C and 1 atmosphere, one mole of an ideal gas occupies about 22.4 liters.

Vm = R T / P, where R is the universal gas constant, T is the absolute temperature in kelvin, and P is the pressure. With R in liter-atmospheres per mole-kelvin (0.082057), pressure in atmospheres, and temperature in kelvin, the molar volume comes out directly in liters per mole.

At the old STP definition of 273.15 K and 1 atmosphere, Vm = 0.082057 times 273.15 divided by 1, which equals about 22.41 liters per mole. Using the IUPAC standard pressure of 1 bar instead of 1 atmosphere gives about 22.71 liters per mole, so the exact number depends on the chosen standard.

For an ideal gas, no. The ideal gas law contains no term for molecular mass or type, so one mole of any ideal gas occupies the same volume at the same temperature and pressure. Real gases deviate slightly because of molecular size and intermolecular forces, especially at high pressure or low temperature.

Enter temperature in kelvin and pressure in atmospheres. The gas constant is a user-editable input preset to 0.082057 liter-atmospheres per mole-kelvin (the CODATA molar gas constant expressed in those units). The output molar volume is given in liters per mole and converted to cubic meters per mole.