Abstract: The invention concerns a device for measuring liquid level, comprising a detection set (Si) including two piezoelectric cells (10, 12) associated with control means for transmitting ultrasonic waves respectively opposite a reference reflector (16), located at a known distance (D) from the associated cell, and from the top surface (14) of the liquid, and processing means for determining the level of liquid by operating on the respective propagation times of the ultrasounds emitted by each of the two cells (10, 12). The invention is characterised in that it comprises means for defining, after the device has been charged, an initialising phase (1100, 1100 bis) during which the control means control the piezoelectric cells (10, 12) such that the ratio between the excitation rate of the reference cell (12) and that of the level-measuring cell (10) is higher than the ratio between those same rates during the subsequent stabilised measuring phase (1300).