Abstract: A method and a gas flow meter for measuring gas flow, having a cylinder, and a piston disposed movably within the cylinder, forming a clearance seal between the piston and the cylinder. A gas flow to be measured is directed to the cylinder so as to move the piston within the cylinder. From the detected movement of the piston, electrical signals representative of the gas flow are generated. Gas temperature and pressure data are also measured. A controller calculates a standardized flow rate of gas based on gas species information, and determines a compressibility factor based on the gas species information and the temperature and pressure data, and calculates a corrected flow rate. The compressibility factor is determined from a table pre-stored in a memory.