An ultrasonic transducer for measuring the travel time of ultrasonic pulses in a gas, in particular for a gas flow rate meter, includes a piezoelectric radial oscillator, which is preferably formed a piezoceramic and which has two sides and electrodes each being disposed on a respective one of the sides for receiving a spike pulse voltage. A first adaptation layer is applied to one of the sides of the radial oscillator. The first adaptation layer has a thickness being less than one-fourth of a characteristic wavelength of the transducer. A second adaptation layer is applied to the first adaptation layer. The second adaptation layer also has a thickness being less than one-fourth of the characteristic wavelength of the transducer. A damping body is mounted on the other of the sides of the radial oscillator. The radial oscillator and the adaptation layers form a sandwich executing a thickness oscillation as a consequence of a radial-thickness coupling, as soon as the spike pulse voltage is applied. The characteristic wavelength of the transducer is a wavelength resulting from natural resonance in the thickness oscillation.