In this study, experimental data for wet- and dry-ground coal samples under wet and dry grinding are characterized by commonly used distribution functions. First, both the R-R and Swrebec functions have superior fitting performances for cumulative particle size curves compared to the other studied functions. On this basis, a time-dependent expression is drawn to describe the cumulative particle size distribution. Second, the R-R function produces a significantly superior fit to the relative mass distributions of the ground products compared to those of the others at a short grinding time. The goodness of fit for all distribution functions studied performs marginally worse at approximately 3 min, which can be associated with a change in the dominant breakage mechanisms from impact to abrasion-chipping. With an increase in the grinding time, the G-G-S function is the optimal function for characterizing the particle size probability mass distributions of wet grinding, whereas the G-M function provides the best fitting performance when applied to the experimental dry-grinding data. Further, the optimal particle size probability density functions are associated with the difference in breakage mechanisms between wet and dry grinding. (C) 2019 Elsevier B.V. All rights reserved.