In the theory of grinding kinetics, the grindability of a material is the only factor used to determine the required size of a grinding machine. So for users of the Tower mill, this grindability is expressed through Bond's work index (W-i). However, the uniformity constant (n), which is found empirically by using a small Tower mill and is expressed also as the grindability of material, can be of great help to designers in the determination of the real parameters of a Tower mill. The present study is an approach to establish a relationship between the Bond's third theory of comminution and the above-mentioned constant of grinding kinetics. The validity of the obtained relationship, [n] = 1.47 -0.309ln[W-i], has been confirmed with a correlation coefficient of 0.855** through a regression analysis of 22 samples of limestone. (C) 2002 Elsevier Science B.V. All rights reserved.