Purpose: To determine the correlation between interpupillary distance (IPD) and innerouter intercanthal distance (IOICD) and to find a regression equation for calculating IPD based on IOICD measurements.Methods: The study subjects were randomly selected from individuals aged 3 months to 20 years who were referred to our ophthalmology clinic, health care centers and children attending kindergartens. Participants were divided into 4 age categories: £3, 3-5, 5-12.5 and 12.5-20 years. IPD was measured by a PD meter (PD2, Oculus, Germany); other parameters including IOICD, nasal limbus to temporal limbus (NLTL), inner intercanthal distance (IICD) and outer intercanthal distance (OICD) were measured using a translucent plastic ruler. Results: The study included 254 female (60.6%) and 165 male (39.4%) subjects with mean age of 87.7±73.2 (range 3-240) months. Significant correlation was observed between IOICD and IPD in the 3-5 yr and 12.5-20 yr age groups. In the £3 and 5-12.5 year age groups, NLTL had the best correlation with IPD. The regression equations for calculating IPD according to IOICD were as follows. In male subjects, near IPD= 0.941×IOICD (r²= 0.98, P<0.001) and for female subjects, near IPD= 0.948×IOICD (r²= 0.98, P<0.001).Conclusion: IPD and IOICD measurements are strongly and positively correlated; IOICD measurements are simpler to obtain and may be used to calculate IPD readings which are more difficult to measure by usual methods in children.