Nowadays, it is desired to use water resources more efficiently due to environmental factors. In this context, the importance of dry stirred mills is increasing day by day. In ball mills, grinding performance can be increased by using media with different sizes and choosing the appropriate grinding media size distribution. It is thought that a similar approach can be applied for dry-stirred mills. Thus, it is predicted that there may be effects on grinding performance and product quality. Although there has been an increasing amount of research on dry stirred mills lately, a missing point is the discussion of the effect of grinding media size distribution. Within the scope of the study, the effect of ball size distribution - a variable that directly affects the mill's performance - on the grinding performance of the vertical dry stirred mill was investigated by batch grinding tests. For this purpose, the bi-modal and tri-modal compositions of the media sizes selected using the material size-ball size ratio values developed in the literature were mixed in different ratios for the vertical stirred mill. The data obtained from the tests performed at different stirrer speeds for calcite, clinker, and copper ores were evaluated in terms of energy, shape of the size distribution, and the obtained size reduction ratios. In addition, the effects of using different sized media distributions on media wear are discussed. It is thought that the findings obtained from the study will be beneficial on the dry stirred mill technology, which is expected to become increasingly widespread. © 2021 Union of Chambers of Engineers and Architects of Turkey. All rights reserved.