A simple theoretical model was used to simulate the changes in particle size distribution that occur when crystals grow, aggregate or disaggregate to a defined extent. The change in total particle volume was used as an index of growth; aggregation and disaggregation were expressed as the change in total particle number. Indices of inhibition of growth and of aggregation in hypothetical test cases were calculated in relation to a control and compared with the inhibition index derived by the standard method of comparing the distribution of particle volume around a given arbitrary diameter on the particle distribution curve. Apparently, the expression of particle growth and aggregation in terms of total volume and number, respectively, is a preferable alternative to the standard technique.