Standard Molar Volume is the volume occupied by one mole of any gas at STP. Remember that "STP" is Standard Temperature and Pressure. Standard temperature is 0 &176:C or 273 K. Standard pressure is 1 atmosphere or 760 mm Hg (also called "torr"). 1 mole of any gas at STP occupies 22.4 liters of volume.
where p is the pressure, v is the volume, n is the number of mole (which can be equal to mass /mr), T is the temperature in kelvin, and r is (molar constant) = 8.31 (units)