The hold-up of a ball mill in operation is dependent on the dynamic porosity of the bed of grinding balls amongst others. For constant hold-up, the greater the volume of slurry held inside the dynamic bed, the smaller the pool volume. It is to ascertain this experimentally that the dependency between pool and hold-up in a batch mill is investigated here. Using a transparent mill of internal diameter 552 mm and length 180 mm, the load behaviour of a 10 mm ball charge filled at 20% of the volume of the mill and run at 60% critical speed was videoed. Six artificial solutions of viscosity between 0 and 60 mPa(.)s were then prepared for testing. The pool angle was measured for a gradual increase in slurry filling from 0 to 3. After analysis, it was found that Shi's phenomenological model of slurry hold-up matched well the measurements. Of note is that the predicted pool level was consistently above the actual one by no more than 8 degrees of angle. The measured mean shoulder and toe angles were also observed to deviate by +5.3 degrees and -12.5 degrees respectively from theory. An attempt to explain this was proposed using the experimental evidence at hand.