Embodiments relate to a system and method for calibrating a ratio of body size of a subject including setting a body coordinate system of each body segment of the subject, calculating a first rotation matrix from a world coordinate system set based on the ground to a sensor coordinate system of each motion sensor when the subject takes a first basic pose, calculating a second rotation matrix from the world coordinate system to the sensor coordinate system of each motion sensor when the subject takes a second basic pose, calculating a third rotation matrix from the world coordinate system to the body coordinate system of a trunk for a first motion sensor attached to the trunk of the subject, and calculating a ratio of body size of the subject based on the third rotation matrix.