Here is your Ball Mill Design/Sizing Procedure. Calculation of top size grinding media (Fred C. Bond) Calculation of top size grinding media AZZARONI's Formula I attach Fred Bond's first empirical equation for sizing grinding balls for ball mills as well as a few other links to good related articles on the topic.

Energy Use of Fine Grinding in Mineral Processing. For example, the figure suggests that a mill operating with an F80 of 100 μm should use 3-mm media, while a mill grinding to below 10 μm would need to use 1-mm media.