Tooth-size assessment is a useful indicator of dental crowding which constitutes one of the main parameters in tooth-size arch-length discrepancy (TSALD). Systematic TSALD evaluation is imperative in all patients consulting for dentofacial orthopedic treatment. The present study aims to compare four measurement techniques for calibrating tooth size. It was performed on casts taken from 30 Moroccan patients consulting at the Dentofacial Orthopedics Department of the Rabat School of Dentistry. Four measurement methods were used to calculate the largest mesiodistal diameter of mandibular teeth mesial to the first molars. Statistical analysis showed that the methods using a digital caliper, the analog vernier caliper and the computerized technique are reliable, accurate, and interchangeable. In contrast, the analog caliper with no vernier is less accurate.