3 Look in a mirror or find a friend
Stand 8 in. (20 cm.) away from a mirror or a friend. Place & hold the PD ruler against your brow. Keep your face straight.
5 Reday. set. measure.
Try to not move your head or the ruler. First open your right eye and close your left eye. Look straight ahead and read the millimeter line that matches up with the center of your right pupil. This number represents your PD in millimeters.