Abstract: The meter has a housing with an inlet and an outlet. The housing is divided between the inlet and the outlet by a partition wall through which a measuring tube with a rectangular cross-section passes. Gas flows through the measuring tube, through which ultrasonic pulses are simultaneously transmitted by transducers disposed on the end walls. The flow rate of the gas is determined from the difference in the time of flight of the bidirectional sound pulses. The gas is directed into the measuring tube through two guidance ducts which run along both longitudinal sides of the measuring tube. Said guidance ducts are also rectangular in cross-section and each contain a flow rectifier.