A semiempirical equation representing the average chip thickness existing during grinding is presented. The scatter of surface finish data obtained using high and low wheel-speeds and wheel-work conformities, fine and coarse dressing procedures and various system spring stiffnesses is greatly reduced when plotted versus average chip thickness. Two metal removal regions, ploughing and cutting, are clearly defined by the finish-chip thickness graph. Altering machine variables in order to reduce the average chip thickness greatly improves surface finish in the cutting region. In the ploughing region, the finish improvements are smaller because the degree of ploughing and grooving of the workpiece possibly affects the measured finish.