A theoretical model for the prediction of the soil–water characteristic curve (SWCC) is presented using pore-scale analysis and three-dimensional approximations of pore geometry employing the concept of unit cells. The model considers the effect of particle size and packing porosity on funicular and pendular retention. The unit cell was upscaled to non-uniform soils using the grain-size distribution curve. SWCC experiments on uniform and graded glass beads were carried out to provide verification data. Predictions for the glass beads showed reasonable results for drying SWCCs. The nonionic surfactant Triton X-100 and sodium chloride were utilized to demonstrate the role of the contact angle and surface tension. The modeling of wetting curves using advancing contact angles indicated the need to consider additional hysteresis mechanisms. The hypothesis of independent grain-size fractions often underestimated matric suctions, leading to the proposal of a correction function using the coefficient of uniformity. The proposed approaches were compared to four previously published models, using 58 glass beads and sandy materials. The new models provided superior results for most of the materials studied. The proposed framework offers a general approach that may be modified in the future by including other retention mechanisms and unit cell geometries.