Surface roughness measurement has been dominated by profilometers for years. The alternative optical methods offer advantages such as non-contact and high speed, therefore, they are more attractive to industries which would like to achieve on-line 100% inspection. In this study, a pair of photodetectors was used to detect the Intensity Ratio (IR) reflected from a ground metal surface, which was illuminated by a white light source. These IR values were plotted against the mechanical surface roughness Ra values and a good correlation was found. This study tested aluminum, brass, copper, stainless steel and tool steel in the roughness range from 0.08 to 2.54 microns (3 to 100 micro inches) Ra. The resulting IR curves varied uniquely.