The diameter of the workpiece is measured, while the workpiece is located on the CNC (computer numerical controlled) turning machine, using a new laser instrument and technique. The optical instrument is based on the laser Doppler principle, using an He—Ne laser as a light source. It obtains data by detecting the scattered light from the surface of a rotating workpiece, processing this data with respect to the rotation of the spindle and providing a value representing the workpiece diameter. The basic resolution of the system depends on the wavelength of the laser and geometry of the optics. Higher resolution can be achieved by obtaining the data from the workpiece surface over more than one complete revolution of the spindle. The resolution for one revolution of the spindle is 0.5μm and for ten 0.05μm. The measurement system is also integrated with the CNC turning machine, particularly for autofocusing of the instrument. The instrument is mounted on the tool holder of the CNC turning machine, which is focused by means of a tool offset parameter for non-contact measurement of each different diameter. Autofocusing is carried out using the MI5 machine tool interface unit which is already established for the Renishaw probe system, according to CNC part programming. The performance of the proposed technique and instrument is verified through the experiments.