amount of space required for the alignment of unerupted permanent teeth in the dental arch. Objective: This study was conducted to compare betw Objective: een the use of study model and digital panoramic radiograph with special computer software program in estimating tooth size and arch length in children. Study design: Study models and digital panoramic ra Study design: diographs with 1:1 magnification factor of one hundred 8-9years old children (50 boys and 50girls) were obtained. On the model, the mesiodistal tooth size of lower and upper permanent central and lateral incisors were measured with an accurate sliding digital micrometer caliper. Upper and lower arch lengths were also measured from the mesial surface of the first permanent molar in one side of the arch to the mesial surface of the contra lateral side using 0.25 inch stainless steel wire. These measurements were then compared to that obtained from the digital panoramic radiograph using special soft ware program (AUTOCAD 2010). The sum of the mesiodistal dimensions of the four permanent mandibular incisors recorded from the models were used to predict the combined sizes of the unerupted canines and premolars using Moyers, method (at 95% evel of probability). These predicted measurements of unerupted canines and premolars were compared to that measured from the digital panoramic radiographs using (AUTOCAD 2010) program. Results: No statistical significant difference was Results: observed between study model and digital panoramic radiograph with 1:1 magnification factor in estimating tooth size and arch length in children of the present study. Conclusion: Using 1:1 magnification digital panoram Conclusion: ic radiograph with special software computer program is an applicable, accurate and effective method for estimating tooth size and arch length.