The geometry of the four-ball test configuration was examined to develop a method to calculate the wear volume of noncircular scars. It was found that the length of the scar normal to the direction of sliding is related to the relative displacement between the upper and lower balls. The width of the scar parallel to the direction of sliding is dependent upon the curvature of the scar normal to the sliding direction. This curvature is a function of upper ball wear, and it is the upper ball wear that causes noncircularity of the lower ball scars.