The pore size distribution calculated using the Washburn equation was evaluated. The pore-sphere network was selected as a model for porous media since this model could qualitatively describe hysteresis and retention phenomena. 3-Dimensional lattices of square configuration were considered with normal, skewed and bimodal pore size distributions. The calculated pore size distribution was accurate up to the average size pores, but significantly different for larger pores. The fraction of average size pores was always exaggerated. Pore connectivity had larger influence on the pore size distribution than the lattice structures.