What is PD?
Pupillary distance (PD), also known as interpupillary distance is the distance between the center of one pupil, the black area of the eye, to the center of the other pupil. This measurement is used in the making of lens and is essential for ensuring that the optical center of your lens aligns with properly with your eyes. If PD is measured incorrectly, it can cause eye strain, dizziness, headaches, and visual discomfort when wearing glasses.
How to measure PD with Help
To measure your PD accurately, you will need a millimeter ruler and a friend to assist you.
Look straight ahead and keep your head still.
Have your friend place the ruler just below your eyes, as close to your face as possible, keeping it completely horizontal.
Align the zero mark with the center of one pupil.
While you continue looking straight ahead, your friend should note the millimeter marking that aligns with the center of your other pupil.
The number recorded is your pupillary distance.
Repeat the measurement once or twice to ensure accuracy.
How to measure PD by yourself?
If you are measuring PD on your own, you will need a millimeter ruler and a mirror.
Stand about 8–12 inches away from a mirror and look straight at your reflection.
Hold the ruler horizontally just below your eyes.
Align the zero mark with the center of one pupil.
Without moving your head, read the millimeter marking that aligns with the center of the other pupil.
The number shown is your pupillary distance.
Repeat the measurement to confirm consistency.
How to Measure Pupillary Distance?
By: Wendy Y.
Last edited: 12/13/2025