How to Measure Pupillary Distance

If you have a prescription for corrective lenses, you might notice the letters PD and a number next to it. These letters and numbers stand for pupillary distance, and it's a vital part of ensuring that your new eyeglasses and lenses are positioned in the correct place for comfortable wear and clear vision. Read on to learn more about pupillary distance and how to measure it yourself at home.

What is PD?

Pupillary distance, or PD, is the measurement of the distance between the centers of your pupils. It's important because it helped to determine how your eyes are positioned when you look through the lens of your prescription glasses. In order to ensure the best prescription, your PD needs to be as accurate as possible. For adults, the average PD is between 54 and 74 millimeters, and for kids, it's typically between 43 and 58 millimeters. Most of the time, your eye doctor will measure to get your pupillary distance at your eye exam. If you don't' receive a PD measurement or you want to purchase new glasses and need this number in order to purchase them, there are a few easy steps you can take to measure the PD yourself.

How to Measure Your Pupillary Distance at Home

If you want to try to measure your PD yourself, you'll need a large mirror and a ruler:

Stand eight inches away from a mirror, and then hold a ruler directly against your brow line.
Close your right eye first, then align the ruler at the 0 mm mark with the center of your left pupil.
Look straight forward into the mirror, then close your left eye and open your right eye.
The mm line on the ruler that lines up to the center of your right pupil is your PD.
Write this number on a piece of paper for future reference.
You may want to repeat the process one or two more times, just to ensure you get an accurate measurement.

If you don't have a ruler handy, there are several places you can download and print one online. Make sure you're using one with mm and not inches.

Single and Dual PD

The term single PD refers to the pupillary distance between the center of one pupil to the other. This can be measured as a distance or near PD. The distance PD is used for prescription glasses, with the exception of reading glasses. You'll need to calculate your PD differently if you need this number for reading glasses since the lenses are completely different from prescription eyeglasses.

Dual PD is also called monocular PD and uses two numbers. The dual PD is the distance between the center of each pupil to the bridge of your nose. You may see dual PD written on your prescription like this: 32/30. The first number refers to the right eye or OD measurement, and the second number refers to the left eye or OS measurement.

How to Measure Pupillary Distance