The invention relates to a device for measuring a mass flow, comprising a measuring wheel (3) that is supported by a shaft (4) and that is driven and impinged axially by the mass flow. Said wheel deflects the flow, giving it both radial and tangential speed components. The shaft bears an actuation spur wheel (7), which engages with an intermediate spur wheel (8) that is held in position by a force measuring device (14) and has a second meshing with a drive spur wheel (9) that is driven by a drive motor (13). The diameter of the actuation spur wheel (7) is more than 0.3 fold, preferably 0.5 to 1 of the diameter of the measuring wheel (3). This provides a device for measuring a mass flow, which has a high zero constant and thus a high degree of measuring precision, is cost-effective to produce, robust during operation and which has none of the disadvantages of prior art.