Metal thicknesses can be determined using optical methods such as spectroscopic ellipsometry when the thickness of the film is small enough that the light penetrates to the bottom of the film. In order to use ellipsometry, it is necessary to determine the optical constants of the film material accurately. In this work, we describe the determination of the optical constants and thicknesses of single metal layers of NiFe, Cu, Co, Ta, FeMn deposited with two different deposition methods. The thicknesses range from about 6 to about 20 nm thick. We have also investigated the ex situ measurement of multiple metal layers, and discuss the conditions where the thicknesses of the individual layers can be determined and the conditions where they cannot be distinguished from each other.