How To Measure Your PD

What is PD?

PD stands for Pupillary Distance. It is the distance, measured in millimeters (mm), between the centers of your pupils.

Why is it important? Your PD ensures that the optical center of your lenses aligns perfectly with your eyes. If this number is wrong, your glasses might cause blurry vision, eye strain, or headaches.

Since PD is often omitted from doctor's prescriptions, here are two easy ways to measure it yourself.

Method 1: With a Friend (Most Accurate)

Having a friend help you is the easiest way to get a precise measurement.

  1. Stand up straight: Stand about 8 inches (20cm) away from your friend.

  2. Look straight ahead: Look at an object in the distance behind your friend (do not look at their eyes or the ruler).

  3. Place the ruler: Have your friend hold a millimeter ruler flat against your forehead, just above your eyes.

  4. Align: Your friend should align the 0 mark of the ruler with the center of your right pupil.

  5. Measure: Without moving the ruler, your friend checks the number that lines up with the center of your left pupil.

  6. Repeat: Measure 2-3 times to ensure accuracy. The average for adults is usually between 58mm and 68mm.

Method 2: The Mirror Method (DIY)

No one around to help? You can do it yourself with a mirror.

  1. Stand 8 inches (20cm) away from a well-lit mirror.

  2. Hold a ruler against your brow line.

  3. Close your Right Eye and align the ruler’s 0 mm mark with the center of your Left pupil.

  4. Look straight ahead.

  5. Close your Left Eye and open your Right Eye.

  6. Read the measurement that aligns with the center of your Right pupil.

  7. Tip: Do not move your head or the ruler during this process; only open and close your eyes.

Dual PD vs. Single PD

Sometimes you might see two numbers (e.g., 32/32). This is a Dual PD (or Monocular PD).

  • Single PD: The total distance between pupils (e.g., 64).

  • Dual PD: The distance from the center of the nose bridge to each eye individually (e.g., 32 right / 32 left).

  • Note: If you have a Dual PD, simply add the two numbers together to get your Single PD (32 + 32 = 64).