Its object is to allow measurement of the volume of fuel (2) using optic fiber cables (3); it is characterized in that, adhered to one or more of the inner faces of the tank (1) there is at least one sheet (4) in which a plurality of optic fiber cables (3) with different lengths are included, located between the inner face of the tank and the sheet (4). One set of the ends (10) of the optic fiber cables (3) are disposed so that they are in contact with the fuel (2) when it reaches their level, thereby allowing measurement of the fuel level at all times.The preferred embodiment distributes the optic fiber cables (3) on two opposing lateral faces of the tank (1) so that they cross over one another and in opposite directions to measure any fuel level.It is applied in aeronautics.