Tool wear progression is inevitable in precision cutting. However, the effect of tool wear on energy consumption at machine, spindle, and process levels is yet to understand. In this study, specific energy in dry milling of hardened AISI H13 was studied at the machine, spindle, and process levels. The effect of process parameters and tool wear progression on energy consumption at each level was investigated. The results indicated that tool wear progression only has a predominant influence on energy consumption at the process level but not the machine and spindle levels. Energy consumption at machine level can be described with a traditional empirical model effectively. However, the traditional model is incapable of predicting energy consumption at the process level. The investigation in energy consumption at different levels can help improve energy efficiency. Since energy consumption at the process level is responsible for chip formation and surface generation, the study of energy consumption at this level is critical to understanding and optimizing of a machining process.