The operating speed of a grinding mill refers to the actual speed at which the mill operates in good working condition.

Currently, the most suitable operating speed n in production is calculated using the following formula:

n = (0.76～0.88)n₀ Production practice has shown that when the grinding media filling rate is 54%, a grinding productivity is higher when the operating speed is set at 88% of the critical speed than at 76%. For fine grinding (feed particle size less than 3mm, grinding product less than 0.1mm), setting the operating speed to 88% of the critical speed is obviously too high and affects quality; it should be slightly lower. Currently, most mineral processing plants operate their grinding mills at around 85% of the critical speed.