Abstract: An apparatus and method for automatically measuring the diameter of a part. A part to be measured is rotated through a plurality of measurement positions by an angle of rotation. A measuring device measures the radial distance from a surface point at each position of the part to the center thereof for each angle of rotation. The distance is calculated between successive points on the surface as a function of the measured radial distance of successive points along the surface and the angle of rotation between the measured points. A plurality of the distances as taken through a complete rotation of the rotational device is summed together to provide a circumference measurement of the part. A diameter measurement of the part is achieved by dividing the circumference by &pgr;.