Results on least-squares refinement of X-ray reflectivity data obtained with a conventional powder diffractometer are reported. A model containing an oxygen contaminated surface on Pt was used to refine experimental data for a “500-Å” Pt film on Si. Values of layer thickness, density, and roughness determined by least-squares refinement agree with those obtained from highresolution reflectivity data. The results were found to be insensitive to the film-surface alignment. An agreement of ±2.3 Å for Pt thickness, 8% for density, and 2.5 Å for roughness was obtained when the surface was aligned to within the divergence of the incident X-ray beam. The least-squares refinement method was also used to analyze two sputtered “300-Å” Pt films deposited at 4 and 20 × 10-6 Torr Ar pressure. Results showed a significant increase in Pt thickness and a decrease in density for the 20 × 10-6 film probably caused by a large amount of Ar trapped in the film.