The particle size distribution of suspensions of fine particles was determined by a photocentrifuge from transmission/extinction profiles. Photocentrifuges provide a useful tool for the characterization and quality control of suspensions. While the variation of the light extinction curves caused by centrifugal segregation allows a qualitative description, a rigorous formulation provides a quantitative characterization. The present work reports on the determination of the particle size distribution using space and time resolved extinction profiles. The particle size distribution is obtained by analyzing the variation of the extinction at any point of the sample over the full centrifugation time or by analyzing the extinction variation over the entire sample length for any centrifugation time span. The advantage of the second method is the potential to save time.