This paper presents a methodology for conceptual aircraft design to evaluate the space available for systems (top-down approach) and to estimate the space required for critical components impacting the aircraft configuration (bottom-up approach). The presented top-down approach introduces the concept of “equivalent design volume”, including the space required for systems and the associated empty space to access, maintain and ventilate them. This approach enables an early feasibility check for aircraft configuration exploration regarding the integration and installation of systems, without having to detail the system architecture. In complement, the bottom-up approach introduces the estimation of the required dimensions for critical components. Here, the example of the flight control actuators integration in the wing tip is presented.