The operation of AG/SAG mills is sensitive to mill filling, therefore developing grindcurves to relate mill filling to performance indicators such as throughput, power draw, and product size can assist in achieving optimal mill operations. The throughput, power draw, and product size have been shown to peak at different mill filling levels. Establishing grindcurves can assist operators to decide on the best set point for operating their mill. Factors such as mill speed, mill inlet water, feed size distribution, and ore hardness all have an influence on the grindcurve, and form an integral part of the optimisation process. Test work has been conducted at a number of sites to develop grindcurves for different mills treating a range of ores. The results show great promise for use in optimising the operating set points for use in mill control. The methodology for developing grindcurves is described and the results from the case studies performed on fixed and variable speed mills are discussed. (C) 2009 Elsevier Ltd. All rights reserved.