The detn. of the wt. per unit area (\"coating wt.\") of phosphate layers on galvanized steel by means of FT-IR-spectrometry has been performed by three different techniques: (i) principal component regression (PCR) of absorption data, (ii) utilizing the thickness dependent wavenumber shift of a band due to a special optical surface effect obsd. with parallel-polarized radiation and (iii) of an interference band obsd. with perpendicular-polarized radiation.