A water suction apparatus has been used to measure capillary pressure curves of glass beads in both loose and dense random packings. Four different mono-sized samples and four ternary mixtures have been examined. It is shown that the experimental results can be reduced to a single curve by means of a correlation based on the specific surface and porosity. This correlation is further validated by experiments with a series of five grades of diatomaceous filter aid. The experimental desaturation process is simulated with a 2D network model of pore space, involving packing based on pore size distributions calculated from the tetrahedral packing model. This gives capillary pressure curves comparable with the experimental results for sphere packing, which correlate with the experimental results. Therefore, the method provides a relationship between grain space and pore space through capillary pressure curves.