A common form for fragment size distributions from blasting is derived from dimensional analysis. When gravity is neglected and the fragment shape is constant, one dimensionless parameter, Π s, remains. If the size distribution uses the quantities x/x max and x 50/x max the dependence on Π s becomes implicit. The Swebrec function has this preferred form. Π s depends essentially on specific charge, explosive energy, burden and rock strength and in a way, which reminds of the x 50-prediction equation of the Kuz-Ram model. A generalization of the x 50-equation is derived, which depends on whether the blasting is 2D or 3D, on the type of loading and on the material model. Test blast results are used to make the appropriate choice. One consequence is that the q-dependence of the x 50-equation changes with the way in which the blasting is done. Another is that the dependence of the Kuz-Ram uniformity index n on geometry only is questionable.