The short answer: Your PD, or pupillary distance, is the distance in millimeters between the centers of your pupils. To measure it at home, stand about an arm's length from a mirror, hold a millimeter ruler flat across your brow, close your right eye and line the zero up with your left pupil, then without moving the ruler read the mark over your right pupil. Most adults measure between 54 and 74 mm.

What PD is and why it matters

Pupillary distance tells the lab where to place the optical center of each lens so it lines up with your pupils. Get it wrong and you can feel eye strain, headaches, or a slight pulling sensation, especially with stronger prescriptions. It is the one measurement a prescription sometimes leaves out, so ordering glasses online often means measuring it yourself.

The mirror method, step by step

1. Stand about 20 cm, roughly an arm's length, from a mirror in good light.
2. Hold a millimeter ruler horizontally against your brow, just above your eyes.
3. Close your right eye. Line the ruler's zero mark up with the center of your left pupil.
4. Keep the ruler perfectly still and your head straight. Now close your left eye and open your right.
5. Read the millimeter mark that sits over the center of your right pupil. That number is your PD.
6. Repeat two or three times and take the average for accuracy.

The two-person method (more accurate)

If someone can help, sit down and look straight ahead at a fixed point across the room, such as a spot on the wall. Have them hold the ruler across your brow and read the distance between the centers of your pupils while you keep your eyes still and focused into the distance. Looking far away keeps your eyes parallel, which is exactly the position glasses are made for.

Single PD vs dual PD

A single PD is one number for both eyes, and it is all most single-vision glasses need. A dual PD splits the measurement into two, the distance from the center of your nose to each pupil, because faces are rarely perfectly symmetrical. Dual PD matters most for progressive and high-power lenses. If your form asks for two numbers, measure from the center of your nose bridge to each pupil in turn.

Common mistakes to avoid

• Tilting your head or the ruler. Keep both level and face the mirror square on.
• Focusing on the mirror instead of into the distance, which pulls the eyes inward and shrinks the reading.
• Measuring pupil edge to edge. Always measure center to center.
• Trusting a single reading. Take the average of a few.

From our test bench. The error we see most is people focusing on their own reflection while they measure, which converges the eyes and reads a couple of millimeters short. The fix is the two-person method with your gaze fixed across the room. If you are on your own, measure three times on different days and average; a real PD does not drift.

FAQ

What is the average PD for an adult?

Most adults fall between 54 and 74 mm, with the average around 63 mm for men and 60 mm for women. Children measure smaller. Because the range is wide, it is worth measuring your own rather than assuming an average, especially for stronger prescriptions.

Can I get my PD from my prescription?

Sometimes. Some prescriptions list PD and some do not, because it is technically a fitting measurement rather than part of the correction. You can ask your optician to include it, or measure it yourself at home with a ruler and mirror using the method above.

Part of Choosing Glasses Frames · Related: the numbers on your frame · Last updated: July 29, 2026