Reduction of the thickness of the diamond-like-carbon (DLC) overcoat deposited on media and head, plays an important role in enhancing areal density. This is because the DLC layer contributes directly to the spacing between media and head and increases in areal density are achieved by reducing this spacing. In fact, nowadays DLC thicknesses of the order of 50 Angstrom are required. With such ultra-thin DLC overcoats, quick and accurate thickness measurements are becoming a must. In this article, an optical technique for measuring the DLC thickness, rapidly and nondestructively is presented. The technique, termed the 'n&k Method,' is based on broad band reflectance spectrophotometry and Forouhi-Bloomer dispersion equations in the data analysis. Results for samples with DLC thicknesses ranging from approximately 25 Angstrom to 300 Angstrom are given. In addition, a typical uniformity map of DLC on a magnetic disk is presented, whereby the thickness ranges from 46 Angstrom to 50 Angstrom, with a mean value of 50 Angstrom, and standard deviation of 2 Angstrom. The determined thicknesses obtained using the 'n&k Method' is compared with those from step height measurements using stylus and atomic force microscopy (AFM). The results are consistent within the measurement error and the optical measurement has by far much better precision and repeatability.