Abstract: The density, volume and mass of fuel held in an aircraft tank are measured by a system of four pressure sensors interfaced with an associated microcomputer. The sensors are disposed in a predetermined array at unequal depths below the surface plane of the contained fuel. Electrical transducers associated with the pressure sensors develop electrical signals representing the associated pressures P1, P2, P3, and P4 and these signals are processed by the microcomputer which is programmed to correlate the individual pressure signals and known coordinate locations of the sensors with certain unknown parameters including the fuel density .rho., and the orientation and distance of the fuel surface plane relative to each pressure sensor. These relationships establish four simultaneous equations that are processed by the programmed microcomputer to yield simultaneous solutions for the density .rho., and for the position of the fuel surface plane.