Investigation of a breakage probability model published by Vogel and Peukert [Vogel, L. and Peukert, W., 2004. Determination of material properties relevant to grinding by practicable labscale milling tests. Int. J. Miner. Process., 74S, 329-338] has led to a modification of their model to describe the degree of impact breakage, t(10). The modified model takes a form similar to the JKMRC prior art breakage model, but with particle size and breakage properties incorporated explicitly in the model. The present breakage model was validated using eight sets of detailed drop weight test data on various types of ore and quarry material over a wide range of impact specific energies and particle sizes. The validation revealed that the present breakage model fits all the data sets well with fewer model parameters. The results from the validation study suggest the present breakage model has a fundamentally better structure for describing the effect of particle size on the breakage distribution function. (C) 2006 Elsevier B.V. All rights reserved.