This study aimed to evaluate the association between maxillary incisor tooth dimensions and gingival phenotype in Thai young adults. Two calibrated examiners examined 400 maxillary incisors from 100 subjects. The gingival phenotype was assessed by transparency probing and visual assessment. Clinical parameters, tooth shape, crown width, crown length, and papilla height were measured. Tooth dimensions were analyzed between tooth shapes. Comparison of tooth dimensions between gingival phenotypes was performed by statistical analysis. The results showed that ovoid, square, and triangular teeth presented with similar tooth proportion (p>0.05). However, a significantly higher papilla height was found in triangular teeth compared with ovoid and square teeth (mean = 4.26±0.65 vs 3.69±0.74 and 3.63±0.78 mm, respectively, p<0.05). The crown length was significantly shorter and tooth proportion was significantly higher in teeth with flat gingival contour than teeth with scalloped gingival contour. Tooth proportion was significantly associated with thin gingival phenotype and scalloped contour gingiva. In summary, there was no difference in tooth dimensions between the tooth shapes evaluated. Lower tooth proportion was found in thin gingival phenotype, thick scalloped- and thin scalloped gingival contour. For clinical assessment, tooth proportion and tooth shape are influenced by papilla height and the gingival contour.