In chemistry, the molar volume of a substance is the ratio of the volume of a sample of that substance to the amount of substance (usually in mole) in the sample. It can be computed as the substance's atomic or molecular weight, divided by its density. The SI unit of molar volume is cubic metres per mole (m³mol^-1).

For an ideal gas, the standard molar volume is the volume that is occupied by one mole of substance (in gaseous form) at standard temperature and pressure (STP) of 273.15 K (H₂O freezing temperature) and 101325 Pa (1 atm). It is 0.022414 m³mol^-1 or 22.42 L/mol and is directly related to the universal gas constant R in the ideal gas law.

Cubic centimetres (cm³), a measure of volume one million times smaller than a cubic metre, are sometimes also used, to give units of cm³mol^-1.

The molar volume is usually given for a solid substance at 298.15 K (temperature of standard state). Apart from temperature and density, it depends on phase and allotrope of the substance.