How to Measure Your Pupillary Distance (PD) at Home

How to Measure Your Pupillary Distance (PD) at Home

Pupillary distance, or PD, is the one measurement you need to order prescription glasses online that is often missing from your prescription. The good news: you can measure it yourself in about two minutes with a mirror and a ruler.

What PD is and why it matters

PD is the distance, in millimeters, between the centers of your two pupils. It tells the lab where to position the optical center of each lens so it lines up with your line of sight. Get it wrong by a few millimeters and you may notice eye strain or a faint "off" feeling, especially with stronger prescriptions.

Single PD vs. dual PD

  • Single (binocular) PD is one number for both eyes β€” for example, 63 mm. This is fine for most single-vision glasses.
  • Dual (monocular) PD gives a separate measurement from the bridge of your nose to each pupil β€” for example, 31.5 / 31.5. It is more precise and preferred for progressive lenses.

The mirror-and-ruler method

  1. Stand about 20 cm (8 inches) from a mirror.
  2. Hold a millimeter ruler flat against your brow.
  3. Close your left eye. Line the ruler's zero mark up with the center of your right pupil.
  4. Without moving the ruler, open your left eye and close your right.
  5. Read the millimeter mark that now sits over the center of your left pupil. That number is your PD.
  6. Repeat three times and take the average.

Even better, have a friend measure for you while you look at a distant object β€” it removes the small error introduced by focusing on the mirror.

What is a normal PD?

Most adults fall between 54 and 74 mm, with the average around 62–64 mm. Children's PD is smaller. There is no "good" or "bad" PD β€” it is just an anatomical measurement.

Can I get my PD from my optometrist?

Yes. In the US and Canada you are entitled to a copy of your prescription, and you can ask the clinic to add your PD. Some will; some treat it as a separate service. Measuring at home is a perfectly reliable backup.

Putting it together

With your PD in hand and your prescription decoded β€” here is how to read your prescription β€” you have everything you need to order. Shop prescription glasses at LensTrove: frames from $1.99, lenses from $19.99, free shipping over $69 in the US and Canada.

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