Pressure loss measurements for packed beds of binary mixtures of angular parallelepipedal particles are reported for a range of Reynolds numbers from 40 to 800. Mixture void fractions generally lay between values for beds of the individual particles, but in two cases were lower than either component void fraction. Particles were found to overlap to a considerable degree in the bed, resulting in a reduction of effective surface area by up to 33%. A modified version of the Nemec and Levec (2005) pressure loss correlation which accounts for particle interference was used to estimate the degree of overlap, and gave values which agreed well with those estimated from photographs of the bed. This provides the means to estimate the effective specific surface area of a particle mixture of known component properties. It is shown that the appropriate parameters to use for a mixture are the volume-surface or Sauter mean diameter and a similarly defined average particle sphericity. (C) 2018 Elsevier Ltd. All rights reserved.