An apparatus for measuring and/or controlling the level of a liquid, specially fuel, contained in a reservoir. The apparatus comprises means supporting a pivot member inside the reservoir, the pivot member comprising a stationary body fixed relatively to the supporting means and a rotary body connected to a lever, the free end of which carries a float. The rotary body includes a permanent magnet and the stationary member houses a magnetic sensor located within the magnetic field of the permanent magnet. Angular movement of the lever produces rotation of the magnet and is detected by the magnetic sensor which emits signals to a micro processor which, in turn, transmits such signals to external processing means. The processing means correlate such signals, which are proportional to variations in the liquid level, to the volume of liquid contained in the reservoir.