 The molar volume of an ideal gas at 100 kPa (1 bar) is
The molar volume of an ideal gas at 1 atmosphere of pressure is

For crystalline solids, the molar volume can be measured by X-ray crystallography.The unit cell volume ("V"cell) may be calculated from the unit cell parameters, whose determination is the first step in an X-ray crystallography experiment (the calculation is performed automatically by the structure determination software).This is related to the molar volume by
where "N"A is the Avogadro constant and "Z" is the number of formula units in the unit cell.