Comparisons are made between three different models for calculating the entropy for separating a polydispersed system of particles from a fluid. These three entropy models provide the efficiency of a separation and the criteria for the separation. Previous models for either monodispersed or regular solution do not provide constrains for the models. The model for calculating the entropy for separating a solid-liquid system of polydispersed particles is rigorous. The rigorous entropy model is then compared to the regular solution and monodispersed models in calculating a separation efficiency and sedimentation criteria. The comparisons of the three models show only a negligible difference in the calculations for the efficiency of the separation and the sedimentation criteria. Hence, the simpler monodispersed model may be used for systems with distributions in particle size.