There is a direct relationship between the efficiency of mechanized excavation in hard rocks and that of disc cutters. Disc cutter wear is an important effective factor involved in the functionality of tunnel boring machines. Replacement of disc cutters is a time-consuming and costly activity that can significantly reduce the TBM utilization and advance rate, and has a major effect on the total time and cost of the tunneling projects. When these machines bore through hard rocks, the cutter wear considerably affects the excavation process. To evaluate the performance of the cutters, first, it is essential to figure out how they operate the rock cutting mechanism; secondly, it is important to identify the key factors that cause the wear. In this work, we attempt to introduce a comprehensive numerical method for estimation of disc cutter wear. The field data including the actual cutter wear more than 1000 pieces and the geological parameters along the Kani-Sib transmission tunnel in the northwest of Iran are compiled in a special database that is subjected to a statistical analysis in order to reveal the genuine wear rule. The results obtained from the numerical method indicate that with an increase in the wear of disk cutter up to 25 mm, the applied normal and rolling forces can be multiplied by 2.9 and 2.7, respectively, and by passing the critical wear, the disk cutters lose their optimal performance. This method also shows that confining pressure will increase the wear of the disc cutter. By the proposed formulation, the cutter consumption rate can be predicted with a high accuracy.