The fuel gage of the present invention uses a combination of (i) one or more load cells or fuel level measuring devices, plus in some cases other sensors which measure the pitch or roll angle of the vehicle or the fuel density, to approximately measure the quantity of the fuel in the tank and (ii) a processor and algorithm, which may be a look-up table or formulae, to correct for the inaccuracies arising from the pitch and roll angles of the vehicle, other external forces or from variations in fuel density. Although several weighing systems are disclosed for illustrative purposes, the invention applies to any method of making an approximate measurement of the fuel quantity (weight or volume) and then using analytical techniques to improve on the measurement.