The comminution behavior of a mill is characterized by the frequency of stress events, and the stress energy, acting at each stress event. Based on this, a comminution result is determined by the number of stress events, and the stress intensity. The product of stress number and stress energy is proportional to the specific energy input. The proportionality factor is the energy transfer factor, which describes the percentage of energy that is used for stressing the product particles. Using the characteriztic numbers based on a few tests, the operating parameters can be optimized and different mills can be compared. The application of the stressing model is shown for stirred media mills.