Calibrating the geometry of a pore-network model is a challenging task if such a model is sought to make quantitative predictions for an experimental porous medium system. Our calibration approach maps a digital representation of a porous medium's microscopic pore geometry onto the size distributions for the pore bodies and pore throats and onto the coordination number of the network. This is accomplished by matching the morphological pore-size distribution and the genus of the network with those of the porous medium. The microscopic pore geometries were obtained by simulating random sphere packings, which match the grain-size distribution and the porosity of the experimental porous media. We obtained good agreement between simulated and measured hysteretic capillary pressure-saturation curves for three porous media. Correlations between pore-body and pore-throat sizes were important to achieve a realistic description of the simulated imbibition scanning curves.