Statement of the Problem: The stability of orthodontic treatment depends on preserving the patient’s pretreatment arch form and arch size during and after treatment.Purpose: This investigation was aimed to study the size and shape of Iranian mandibular dental arch and evaluate the correlation of their average dental arch with commercially available preformed rectangular nickel-titanium arch wires.Materials and Method: In this study, 148 subjects were selected among students of Shiraz University of Medical Sciences. The inclusion criteria were having Angle class I in molar and canine relationships, and normal growth pattern. Intercanine and intermolar widths were measured after scanning their mandibular dental casts. Three main arch form templates; square, ovoid and tapered (Orthoform TM; 3M, Unitek, CA, USA) and 12 commercially available preformed mandibular nickel-titanium arch wires were scanned. Intercanine and intermolar widths of arch wires were compared with dental arch widths of the study samples. Arch width, arch form and the most appropriate arch wire were determined for each cast. Student’s t-test was used to compare arch widths and arch depths of male and female subjects. Coefficient of variance was used to determine the variability of indices in the study samples.Results: Most preformed arch wires were wider than the average width of the normal Iranian dental arch. The most frequent arch form in Iranian population was tapered. Inter molar width was the only statistically significant variable between males and females.Conclusion: Variation in available preformed arch wires does not entirely cover the range of diversity of the normal dental arch of our population. Narrow arch wires with a tapered shape are better consistent with the Iranian lower arch.