Design engineers generally use Bond Work Index and Bond energy equation to estimate specific energy requirements for ball milling operations. Morrell has proposed different equations for the Work Index and specific energy, which are claimed to have a wider range of application. In this paper an attempt has been made to provide a comparison of these two approaches and bring out their shortcomings. It has been shown that it is possible to develop a modified approach based on the well proven Kapur energy-size relationship and the size-mass balance mathematical modelling approach. Several important points have been illustrated using our own experimental data and a large amount of relevant data available in the literature.