This paper presents a new approach for determining the specific energy requirement of tumbling mill (grinding) circuits. It is used to demonstrate that there is no significant difference between the energy utilisation efficiency of any of the grinding circuits of the plants studied. Laboratory test results are also presented which indicate that classifier efficiency and recycle load in closed ball mill circuits can have a significant influence on the apparent energy utilisation efficiency. The experimental data indicate that this is achieved through changes to the gradient of the size distribution of the final product. (c) 2007 Elsevier Ltd. All rights reserved.