Drop weight tests are a useful tool to determine energy-size reduction relationships for breakage of particulate materials. Their use in modeling and simulation of size reduction operations has increased significantly in recent years. The main limitation of the classical drop weight test lies in the fact that it does not allow the direct measurement of the fraction of the input energy that is used in particle breakage (called comminution energy). A procedure that overcomes this limitation through the calculation of the comminution energy and the coefficient of restitution in drop weight tests is proposed in the present study. It uses force-time histories of the entire event measured in a modified drop weight apparatus, the Ultrafast Load Cell, along with assumptions of conservation of energy and momentum during impact. Calculations using the procedure have been compared to measurements of the coefficient of restitution using high-speed video, and the agreement is excellent. Experimental results show that the fraction of the input energy that is actually used in particle breakage increases with an increase in relative impact energy and decreases for more elastic and crystalline materials.