A weight measurement system calculates the gross vehicle weight of a helicopter while in hover or level unaccelerated forward flight by measuring and averaging the distances 20,22 between the fuselage 24 and the underside of each main rotor blade 26 at the front and rear of the fuselage 24, measuring the main rotor speed, and correcting for the effects of vertical and horizontal drag forces on the fuselage due to the spinning rotor and forward velocity, respectively, using predetermined vehicle calibration data. An inhibit signal 54 may also be provided to the weight calculation logic to disable the weight calculation when the vehicle is in a flight regime not suitable for accurate weight measurement.