This paper presents a novel optimal redundant inertial sensors configuration in SINS with overall considerations of reliability, navigation accuracy, size and cost of system. The optimal number of redundant sensors is determined by considering the reliability and cost. Based on D-optimality criteria and real code genetic algorithm (RCGA), a novel optimal redundant configuration scheme is established. The experiment results show that the proposed redundant sensors configuration achieves required accuracy with smaller size which is 26.4% of the widely adopted redundant dodecahedron configuration. The optimal experiment method proposed in this paper has been proved to be simple and efficient for designing redundant sensor configuration.