Based on the widely used soil pore classification systems, soil pore ratios α, β and γ were derived. α, β, and γ represent ratios of the fine capillary porosity, coarse capillary porosity, and non-capillary porosity to the effective porosity, respectively. The parameters ψ m and σ of the soil water retention model developed by Kosugi were related to these pore ratios, and a simple method was suggested to estimate ψm and σ from measured soil pore ratios. By analyzing the observed retention data sets of forest soils, it was shown that the soil pore ratios are effectively used to evaluate the soil pore radius distribution. A coordinate system with log(− ψ m) on the abscissa and σ on the ordinate, which represents the constant α, β, and γ lines, was developed as a new diagram to evaluate the soil pore radius distribution in connection with the soil water retention characteristic. Then, the saturated hydraulic conductivity K s of forest soils was correlated with the parameters ψ m and σ, and with the ratios α, β, and γ using the coordinate system and the triangle diagram. Results showed that K s is higher for the soil with a greater median and with a greater width of the pore radius distribution. K s increases as the non-capillary pore ratio γ becomes greater and the coarse capillary pore ratio β becomes smaller. Functional relationships between K s and the water retention parameters, and between K s and the soil pore ratios were derived based on Mualem's model.