A device for checking the quantity of gasolines, Diesel fuels, fuels or liquids in general during introduction in a tank, comprising at least one ultrasound emission source and at least one ultrasound receiver, said ultrasound emission source being arranged so as to send a train of sound waves toward the free surface of the liquid that is present in said tank and to receive a sound beam reflected by said free surface of the liquid, the ratio of the speed of the sound waves with respect to the time between the emission of said sound waves by said ultrasound source and the reception of said sound waves providing a distance that constitutes a datum for calculating the quantity of liquid introduced in the tank.