Pupillary Distance (PD)

PD or pupillary distance is the distance from the center of the pupil (the black spot in the eye) of one eye   to the other in millimeters (mm).This measurement refines the positioning of your lenses within the frame you have chosen. It can be provided in minutes by your optician or doctor, and so we recommend that you ask for it when you have your vision checked. Alternatively, you may ask someone to measure it for you but advise them to be at about an arm's length away from you.

To measure your Pupillary Distance (PD)

Place a regular ruler on the bridge of your nose. Have a friend face you about arms length away. Have your friend measure the distance between the centers of your pupils (the black dots in the middle of your eyes). Or you can do it yourself simply by looking in the mirror. If you need your glasses on to do this, you can draw dots on the lenses where your pupils are (using a magic marker or highlighter); then take the glasses off and measure the distance between them.

It's simple -- like playing connect the dots! 

Remember, PD number is in millimeter.s

As a guideline:

Most adults' PD's are between 55-65. Most kids' PD's are between 42-54.