The volume occupied by one mole of a substance is called its molar volume. Molar volume is denoted by Vm. Molar volume of a substance depends upon temperature and pressure. Molar volume of all gaseous substances at 273K and under 1 atmosphere pressure (NTP conditions) is found to be 22.4 L or 22400 ml. Thus, one mole of any gaseous substance at 273 K and 1 atmosphere pressure occupies a volume equal to 22.4 L or 22400 ml. The unit of molar volume is liter/mol (L/mol), or milliliter/ mol (ml/ mol).