The results of discrete element method simulation were compared with actual grinding experimental results. The grinding rate constant K can be expressed as K=a exp(bn), where n is the rotation speed. To investigate the correlation between K and the simulation results, a new factor, the calculated force, was defined as F-cal=average force acting on a ball coordination number. K could then be expressed as K=a'F-cal+b' and is thus one-dimensionally proportional to F-cal K was found to be correlated with the forces acting on a ball and its contact points. Experimental results confirmed that F-cal is suitable for use as a factor for expression of K.