How to Measure PD

An average PD measurement is about 62mm for women and 64mm for men

With a Friend's Help

You willl need a ruler that measures in millimeters.
Rest the ruler on the bridge of your nose with the 0 millimeter mark centered with your left pupil. Make sure to look straight ahead as your friend measures the distance from the center of your left pupil to the center of your right pupil.
Now you have your pupil distance measurement. 

By Yourself in a Mirror

All you need is a mirror and a ruler that measures in millimeters. Once you're ready, face the mirror and hold the ruler up against the bridge of your nose.
Look straight ahead and align the 0 millimeter mark with the center of your left pupil. Measure the distance from the center of your left pupil to the center of your right pupil.
Now you have your pupil distance measurement.