Pupillary distance (PD) measures the distance between the centers of your pupils. This measurement is used to determine where you look through the lens of your glasses and should be as accurate as possible. The average adult’s PD is between 54-74 mm; kids' are between 43-58 mm. Your eye doctor will usually measure your PD during an eye exam. However, if it was not given to you, the below 5 steps will help you measure it yourself.