Abstract: The invention relates to a device for measuring fuel consumption of liquid-fuel engines with variable power yield depending on operating conditions, especially the fuel consumption of automotive engines, characterized by one fuel metering unit each for return fuel flow and/or forward fuel flow, consisting of: a pair of circular chambers; a freely rotating gear, located within each said chamber; tangentially arranged holes extending into each circular chamber and acting as entry and outlet ports for fuel; a light transmitting component, located in the wall of each chamber and closing the chambers in the zones of the teeth of a ring gear; an infra-red transmitter and an infra-red receiver external to each chamber on one optical axis with the light transmitting components; and a measuring circuit connected to each infra-red receiver, and including a pulse transformer and a comparison circuit.