Your prescription may tell you your PD. But if the PD is not available, use your friend or a mirror to help you figure it out.
MEASURING YOUR OWN PD
HAVING A FRIEND MEASURE YOUR PD
If a friend is measuring your PD, keep both eyes open and have your friend put the zero on the millimeter ruler over the center of one pupil, then measure the distance to the center of the other pupil.
TIPS WHEN A FRIEND IS MEASURING:
•Have them crouch/sit while you stand so they are out of your field of vision.
•Keep your eyes as still as possible.
•Look above his/her head at something approximately 10-20 ft. away.
•Do not look at the person measuring!