Abstract The lack of consolidated preliminary design techniques coping with the characteristics of most recent electric and hybrid-electric power plants is often an obstacle for aircraft manufacturers and for owners and operators as well, making the design process less straightforward and hampering comparisons with respect to more traditional designs. In this paper, a technique for the preliminary weight sizing of electric aircraft in the General Aviation category is explained. This is based on existing procedures typical to conventionally-powered aircraft, integrated in a common framework to suitably tackle the issues raised by the peculiar features of electrically-powered aircraft. Then, an expansion of the design method to the case of a series hybrid propulsion system is investigated. Results in virtual environment on a realistic design are also presented.