Sputtered thin film and multilayer x-ray mirrors are made at the Advanced Photon Source (APS) deposition lab for the APS users. Film thickness calibrations are carried out using in situ and ex situ spectroscopic ellipsometry, interferometry, and x-ray reflectometry. Here, we present a systematic study of thickness and optical constant determination of sputtered thin films of Au, Pt, Pd, Rh, Cr, Cu, as well as W and C, using in situ ellipsometry. Multiple data sets were obtained for each film material with incremental thicknesses and were analyzed with their correlation in mind. Results are compared with those obtained froth interferometry and x-ray reflectivity measurements. The applications and limitations of spectroscopic ellipsometry for metal thin films are discussed. Observations of a relaxation effect of a Rh/Si film and a difference in growth mode in the Cr/Si system compared with other metal/Si systems are presented. [S0734-2101(99)01605-X].