Milling efficiency determination is a challenging task. Most of milling efficiency estimation methods showed low efficiency value that does not exceed 5% as a result of an imprecise common estimation from the difference between the energy input and the generated heat. In this paper, an innovative method for milling efficiency calculations based on the particle deformation process was proposed. It depends on calculating the strain energy that resulted in particle deformation, unlike the particle breakage process, where the number and volume of particles are unchanged. The results indicated that a high mill efficiency closer to 100%, unlike the previous studies, can be obtained at short grinding times. It is also found that there is a certain combination of mill speed and ball size that can lead to highest efficiency due to loading regime and resulted strain energy. More interestingly, the mill efficiency is lower, similar to reported in the literature, at high milling speed, bigger ball sizes, and longer grinding time due to particle breakage where the strain energy is lower.