Grinding slurries are known to be non-Newtonian. For such suspensions,slurry viscosity is not a constant, but is a function of shear rate. This studywas aimed at the derivation of an estimattime of a typical shear rate rangeinside a ball mill, in order to determine appropriate values of apparentviscosity for studies of the effects of rheology on grinding. Shear rates wereestimated by considering the ball charge motion inside the mill.