In chemistry, the molar volume Vm of a substance is the ratio of the volume V of a sample of that substance to the number of moles n in the sample: Vm = V/n.  Apart from computing molar volume by dividing the volume of the substance by the number of moles of substance, it can also be computed as the substance's molar mass divided by its density. Indeed, if the molar mass of substance X is M(X) [kg/mol] and the density of a sample of X is ρ [kg/m3], then the molar volume of X is given by Vm = M(X)/ρ [m3/mol].
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 (0C) and 101325 Pa (1 atmosphere or 760 torr). It is 0.022413 m³mol-1 or 22.413 L/mol and is directly related to the universal gas constant R in the ideal gas law.
- The ratio of the volume and the mass of a sample is the specific volume of the substance—the inverse of density.
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