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The actual flow rate is the volume of a gas somewhere in the system, independent of its density, that flows through a certain point. The term actual flow rate is not clear, when it comes to the mass of a gas flowing through a given point, because gas is compressible. If the pressure is doubled, then for an ideal gas, the mass which flows at a constant flow rate through a particular point is also doubled. To take this enlarged mass flow into account, for gases usually the standard volumetric flow is used, because this is based to certain standard conditions and is thus comparable to the mass flow. In compressed air the standard usually is at 1 bar absolute and 20 degrees C.