Two-dimensional simulations of packed beds composed of binary and ternary particle mixtures were made and image analysis of the bed structure was used to determine the bed porosity and tortuosity. Both the porosity and tortuosity were found to be dependent upon the volume fraction of the large particles. However, the volume fraction alone does not totally determine either the porosity or the tortuosity. For a bed of two different sizes of particles, its tortuosity may be considered a product of two quantities, the macro- and micro-tortuosity, each of which can be determined from the corresponding monosized particle beds.