An apparatus is provided for determining the quantity of fuel in a fuel tank having a contoured interior wall. The apparatus includes a buoyant member for floating on the top surface of fuel in the fuel tank, a conductor supported on the buoyant member to float therewith, and a pattern of resistance in electrical contact with the floating conductor. The pattern of resistance is selected to correspond to the contour of the interior wall. Thus, the resistance pattern is coded to represent the volume profile of the fuel tank. A voltage is applied across the conductor and the pattern of resistance. The floating conductor and the pattern of resistance cooperate to provide a value of resistance corresponding to the depth of fuel in the fuel tank at the measurement location. An indicator interprets that value of resistance to determine the instantaneous quantity of fuel in the fuel tank.