A 5-horsepower Pitt Mill prototype has been used to develop information on the effects of coal characteristics and of mill design and operation on the cost of grinding coal to the 10 microns size range. Grinding media wear is the largest cost factor in fine grinding of coal using stirred bed technology. The specific media loss rate, pounds of media per kW-hour energy input to the grinding bed, more than doubles and the cost per pound of replacement media increases by a factor of four as the chrome steel grinding media ball size is reduced from 3/8 inch to 3/16 inch diameter. The specific media loss rate has been found to be directly related to the ash level of the coal. Estimates of the cost to grind 50 HGI coal to sizes between 10 and 20 µm in the Pitt Mill range from $29 to $10 per ton respectively.