Single-particle breakage is the most efficient size reduction method, as energy losses by friction and unsuccessful impact events are minimized or avoided altogether and losses due to particle-particle interactions do not exist. A simulation procedure for calculating the energy spent in comminution by impact using a sequence of ideal breakage stages on individual particles is analyzed. It is capable of accounting explicitly for the breakage probability, the breakage distribution, the weakening that particles undergo by repeated loading and the stiffness of the media. The procedure has been used to compare different routes for size reduction of selected materials and to assess the energy efficiency in ball milling. It was observed that the lowest energy consumption was achieved with the application of impact energies that follow a power-law relationship with particle size. It was also found that the influence of the stiffness of the tools was only significant for comminution of materials that presented high stiffness. It was also found that the energy efficiency of the Bond ball mill grindability experiment for cement clinker was about 30%. (C) 2004 Elsevier B.V. All rights reserved.