The longest bone in human body is called femur. It is the only bone in upper leg. It the longest as well as the strongest bone in human body . On an average the length of femur is 26.74% of a person's height . It is slightly arched in shape and has 2 parts i.e. upper part and lower part. It is little broader in the upper part but the lower part of the femur is bigger than the upper part of the femur. It acts as an attachment point for all the muscles that exert force over the hip and knee joints