A method of measuring the weight of an aircraft is disclosed. The method comprises, in a self-propelled aircraft undercarriage having a electrical rotating machine, the steps of: measuring the current and voltage going into the rotating machine using current and voltage measuring means, calculating the power into the rotating machine, measuring the speed (or torque or acceleration) of said machine using speed sensing means, and comparing the power and speed (or torque or acceleration) results with a database of power and speed relationships of comparable aircraft of varying weights.