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.