Abstract: In a device for measuring the breath volume of patients, a pair of temperature sensitive sensors are arranged in a tube-like housing of a respiration conduit of a respirator. The sensors are spaced from one another in flow direction and an air resistance member is arranged between them in such way that at least in one of the opposite air flow directions one of the sensors is in a position sheltered from the air flow by the air resistance member. Both of the sensors are connected with electronic circuits respectively and a current supply for holding the temperatures of the sensors on constant high levels. A calorimeter unit is connected to the circuits measuring the current supply necessary to compensate the temperature decrease of the sensors caused by the cool respiration flow. The air throughput is calculated in dependence on the measured current supply.