Your pupillary distance (PD) is the distance in millimeters between the centers of your two pupils. You need it to order glasses, especially online, and you can measure it yourself at home with just a mirror and a millimeter ruler. The average adult PD is about 63 mm, with most people falling between 50 mm and 70 mm.
How to Measure PD at Home
The U.S. Department of Veterans Affairs recommends this method, and it takes about two minutes:
- Stand about 8 inches from a mirror.
- Hold a millimeter ruler against your brow.
- Close your right eye and align the ruler’s 0 mm mark with the center of your left pupil.
- Look straight ahead, then close your left eye and open your right eye.
- Read the millimeter line that falls on the center of your right pupil. That number is your PD.
Repeat this three or four times and average the results. Your readings should be within 1 mm of each other. If they’re jumping around by 2 or 3 mm, you’re likely shifting the ruler between attempts. Keep it pressed gently against your brow so it stays in place.
Binocular PD vs. Monocular PD
The method above gives you a binocular PD: a single number like 63 mm that represents the full distance between your pupils. This works fine for most single-vision glasses.
Monocular PD splits that into two numbers, measuring from the center of your nose to each eye separately. You might get something like 31/32 mm. Most people’s faces aren’t perfectly symmetrical, so these two numbers often differ by a millimeter. Monocular PD matters most for progressive lenses, bifocals, and other multifocal designs because each lens has a narrow corridor that needs to align precisely with that specific eye. To measure monocular PD at home, use the same mirror method but note where the bridge of your nose falls on the ruler, then read the distance from that point to each pupil individually.
Why Accuracy Matters
For standard single-vision lenses, being off by a millimeter in your PD rarely causes noticeable problems. Progressive lenses are far less forgiving. The manufacturing tolerance for progressives is 1 mm per eye, but an error on one side can effectively shift the reading zone by 2 mm on the other eye. Even that small misalignment can make reading uncomfortable and reduce the usable area of the lens.
If your prescription includes progressives, bifocals, or a significant difference in correction between your two eyes, a professional measurement is worth the effort. Opticians use instruments called pupillometers that measure to a fraction of a millimeter, and the process takes seconds.
Getting Your PD From Your Eye Doctor
Many people assume their PD is on their prescription, but it often isn’t. Under the FTC’s Eyeglass Rule, eye doctors must give you a copy of your prescription after an exam, but PD is not a federally required field on that prescription. Some states do require it, and the FTC has encouraged doctors to include it voluntarily, noting that patients who want to buy glasses online will need it.
If your doctor measured your PD during your exam, you can request a copy. Federal and state medical records laws generally entitle you to your own health data, though the process may involve a formal records request rather than a quick phone call. Some offices charge a small fee. If you’d rather skip the hassle, measuring at home or asking an optician at a glasses retailer to measure it for you (often free) are both practical alternatives.
What Counts as a Normal Range
Adults typically fall between 50 mm and 70 mm, with 63 mm being the average. A small percentage of adults have a PD as narrow as 45 mm or as wide as 80 mm. Your PD changes during childhood as your skull grows but stabilizes once you’re fully grown, so adults generally only need to measure it once unless they want to double-check an old number.
If your measurement falls well outside the 50 to 70 mm range, measure again carefully before assuming it’s accurate. An unusual reading is more often a measurement error than an unusual face. If you consistently get the same number, it’s likely correct, and online retailers that let you enter a custom PD will accommodate it.