Background: In Korea, fetuses are currently assessed using ultrasound data collected from foreign subjects. This study aimed to propose independent reference values for the transverse cerebellar diameter (TCD) in Korean fetuses to predict gestational age (GA) and compare the TCD values among different countries. Methods: A total of 1819 healthy singletons with GAs of 15–37 weeks were retrospectively analyzed. The TCD was measured in the transcerebellar plane of the fetal head. TCD percentiles were calculated for different GAs, and a regression model was created to predict GA. Bland–Altman analysis was performed to examine the differences in the mean TCD and variations in the TCD among different countries. Results: The TCD ranged from 1.48 to 4.76 cm with a mean of 2.7 \pm 0.91 cm. In the regression model of TCD (cm) = 0.129 GA (weeks) – 0.527 (95% confidence interval 0.129–0.130, p 0.001), the TCD explained 98.4% of the variance in GA. Significant differences in the mean TCD were found between Korea, the United States, the United Kingdom, Hong Kong, and India. TCD variations increased as the mean TCD increased. Conclusions: Fetal TCD is an important biometric index for predicting GA. Ethnic differences must be considered when using fetal TCD.