A study of the structural design of large SAG mills is presented. Stress ranges from strain gauge measurements are compared with those calculated using finite element models for two mills. The agreement between measurement and calculation for one mill is substantially better than it is for the other. The cause of the discrepancy in agreement between measurement and calculation for the two mills is determined to be the relative percentage of ball charge to total charge. For lower total charge to ball charge ratios, the pressure on the heads or end walls of the mills reduces dramatically. As this ratio increases, the pressure on the heads increases to approach a hydrostatic load. The problem of poor agreement between mill finite element models and fatigue design codes is thus partially resolved. (C) 2011 Elsevier Ltd. All rights reserved.