A considerable body of experimental data now exists on laboratory- and full-scale high pressure rolls which indicates that they offer considerable energy savings over conventional mills such as ball mills. It has been proposed, from experimental data obtained largely from studies on minerals, that the product size distributions from such rolls can be normalised and that a linear relationship is demonstrable between the reduction ratio and the specific energy expended. It is demonstrated here over a wide range of minerals and ores that these propositions are tenable, However, in certain cases, they do not appear to hold. The effect of moisture on these relationships was examined and found not to be significant. Variation of the roller speed does at times affect these relationships while variations in the feed size distributions significantly affect the grindability constants. The utilisation of both relationships in the modelling of high pressure rolls performance was undertaken and generally found to provide reasonable first approximations.