BACKGROUND: Tooth size discrepancies and their absence is considered as the seventh key of an ideal occlusion. The effects of these discrepancies on the occlusion can be determined by measuring the mesio-distal widths of the upper and lower teeth. Bolton’s method calculates the amount of tooth size discrepancies based on sum of the mesiodistal widths of the maxillary and mandibular teeth and substitutes those values in a mathematical formula. Since, the Bolton’s method was initially developed based on the normal occlusion of the Caucasian population, their applicability in different malocclusions and populations needs to be studied further. AIM: The aim of this present study is to assess tooth size discrepancies among individuals with Class I, Class II, and Class III malocclusions in the Coimbatore population using Bolton's analysis. MATERIALS AND METHOD: This observational study was carried out in 150 pretreatment study casts of individuals, aged in the range 13-24 years with no history of previous orthodontic treatment. Included patients were divided into four Angle’s malocclusion groups; Class I; Class II division 1; Class II Division 2; and Class III. Anterior, posterior and overall ratios were calculated and the values obtained were tabulated and then statistically analysed. Percentage of mean values of measured ratios that falls within the 2 Standard Deviation of Bolton’s ratio was also noted. The level of significance was set at 95 % confidence interval (p < 0.05) RESULTS: The mean value of overall ratios were 91.14 ± 3.52, 90.94 ± 4.82, 89.62 ± 3.10, and 90.51± 3.89 for Angle’s Class I, Class II Division 1, Class II Division 2, and Class III malocclusions, respectively. Similarly, Anterior ratios were 77.47 ± 6.58, 76.97 ± 6.27, 76.17 ± 8.93, 75.32 ± 6.01, for Angle’s Class I, Class II Division 1, Class II Division 2, and Class III malocclusions, respectively. Posterior ratios for the were 104.29 ± 6.46, 105.82 ± 6.45, 102.85 ± 9.13, and 106.2 ± 15.01 for Angle’s Class I, Class II Division 1, Class II Division 2, and Class III malocclusions, respectively. The amount of TSD that was outside the Bolton’s ratio was described in percentages as 68% for ± 1 SD, 31 % for ± 2 SD, and 1% for > 2 SD. CONCLUSION: The results of this study suggests that the mean values for anterior, posterior, and overall ratios were similar to that of established Bolton’s ratio, thereby stating the applicability of the ratios with modified values specific to Coimbatore population. It is necessary for the clinicians to use Bolton’s ratio in their practice as it would aid in providing better treatment outcome and meet the treatment expectation by both the orthodontist and the patient. Although variations exist among different population, future studies should be directed towards assessing the variability of these ratios and formulating values specific to a population.