A device for measuring the volume flow of a gas in a duct for making it possible to effect adjustment or balancing at the manufacturer's location and then being installable in a duct at any desired location without leading to varied measurements by providing a plurality of evenly distributed polygonal collecting pipes with unilaterally arranged flow entrance ports connected with a compact unit. A flow baffle is arranged at the entrance point of the collecting pipes, and a nozzle is arranged downstream of the flow rectifier. The measuring probe is located downstream of the nozzle in the measuring unit.