An ultrasonic densimeter for measuring the specific density of a fluid, the densimeter being constructed as a measuring element integrally formed on a fluid channel for the fluid to be evaluated. The measuring element (M) contains a single transmitting/receiving transducer for ultrasonic waves in the form of a piezoelectric disc (1), which serves to generate an ultrasonic wave lobe, which is directed onto the surface of the fluid to be measured and onto a reference interface, and to receive both a reference echo and a useful echo. The measuring element (M) is essentially frustoconical, the piezoelectric disc (1) being arranged on a first conical section surface (1/2), of small diameter, of the measuring element (M) and is preferably perpendicular to the axis of rotation of the measuring element (M), and a second conical section surface (4) of large diameter, which is preferably perpendicular to the axis of rotation of the measuring element (M), being directed onto the fluid to be evaluated. The measuring element (M) is divided perpendicular to its axis of rotation, the first part (2), facing the piezoelectric disc (1), of a first length (L1), of the measuring element (M) consisting of a first material (M1), and the second part (3), facing the fluid, of a second length (L2) of the measuring element (M) consisting of a second material (M2), and the interface (2/3) between the first material (M1) and the second material (M2) serving to generate reference echoes (iref). The ratio of the lengths (L1, L2) is selected such that the reference echos (iref) and the useful echos (ifluid) strike the surface of the piezoelectric disc (1) separated in time in such a way that they can be distinguished for the purpose of an evaluation operation. <IMAGE>