Ball size distribution is commonly used to optimise and control the quality of the mill product. A simulation model combining milling circuit and ball size distribution was used to determine the best make-up ball charge. The objective function was to find the ball mix that guarantees maximum production of the floatable size range (i.e. −75+9μm) applicable to a platinum-bearing ore.The simulated product size distributions were found to display a close match with the measured product from an operational mill. Based on the maximum production of floatable particles, the best combination of make-up ball size was determined in relation to feed flow rate, feed size distribution and ball filling.