We discuss the optimum design issue for tracing type legged robots in the sense that it can jump as high as possible. By applying dimensional analysis techniques, we introduce four non-dimensional parameters that control the jump ratio(= h/l) for a jumping robot. An interesting observation is that there exists the optimum design point where the jump ratio becomes maximum. Through experiments, we found that the robot with the optimum design specification can achieve the jump ratio of 3.6, while the jump ratio decreases for other design points.