© 2018 IEEE. The process of designing bio-inspired knee joint for prosthetics/exoskeletons has been a challenging issue due to the complicated relationships between the performance criteria and the link lengths of the design space, or workspace in the case of manipulators. This paper address this issue by presenting numerical analysis and design methodology that have been used for mapping the design space of a bio-inspired knee joint. Four aspects of performance are modelled: peak mechanical advantage, RMS (root mean square) mechanical advantage, RMS sliding ratio, and range of movement. The performance of the joint is dependent on the shape of the condylar surfaces and the geometry of the four-bar mechanism. The results of the complete map for the design space are characterized by the mechanical advantage, sliding ratio and the range of movement that mimics the human knee joint with the movement of rolling and sliding between the condylar surfaces of the femur and tibia. Therefore, several design charts are proposed accordingly to facilitate the selection of designers of the optimal configuration adapted to their specific application. Based on our numerical analysis performed on the proposed bio-inspired knee joint model, the performance maps demonstrated that there is an estimated reduction of 30% for the actuator required force.