When you set out to order a pair of prescription glasses online, you’ll be asked to provide your pupillary distance. If you’re unsure what this term means, don’t worry—we’ve got you covered!
This article will explain what pupillary distance is, why it’s important, and how to measure it. Here’s what you need to know.
What is Pupillary Distance?
Pupillary distance (PD) is the space—measured in millimeters (mm)—from the center of one pupil to the center of the other.
Knowing this measurement is essential when ordering a new pair of prescription glasses, as it determines where the optical centers on each lens should be placed. In other words, it ensures the prescription power aligns with the centers of your eyes.
Without correctly measuring your pupillary distance, you'll essentially be looking through the wrong part of the lenses. This can result in effects like blurred vision, double vision, headaches, fatigue, and nausea.
For adults, the average pupillary distance is about 63 mm, but you don’t want to assume yours will be the same. Pupillary distance can vary widely—between about 51 mm and 74 mm for women and about 53 mm and 77 mm for men.[*]
How Do You Measure Pupillary Distance At Home?
The best way to get an accurate pupillary distance measurement is by going to an optometrist for an eye exam. Just be sure to ask them to include the PD measurement on your prescription, as it’s not always automatically included. Or visit your local optical store - some opticians will measure it for you with a pupilometer, either at no cost or for a small fee. These are the two most accurate ways to measure.
However, if you don’t want to (or can’t) visit an optometrist, there are many ways to measure your pupillary distance at home yourself! Though not exact, these methods will get you somewhat close to what your actual PD is. These include:
#1 With a Ruler
To measure your pupillary distance using a millimeter ruler and mirror, follow these steps:
- Stand about 8 inches from a mirror.
- With your eyes open, hold the ruler horizontally against your brow bone.
- Close your right eye and line the 0 mm mark up with the center of your left pupil.
- Without moving the ruler, open your right eye and close your left eye.
- Read the millimeter line aligned over the center of your right pupil. This number represents your approximate pupillary distance.
- Re-measure three times to ensure accuracy.
#2 With Prescription Eyeglasses
If you’re wondering, “Can you measure PD from old glasses?” the answer is yes! All you need is your glasses, a mirror, and a non-permanent marker.
- Wearing your glasses, stand about 8 inches away from a mirror.
- Close your right eye.
- Using your left eye, focus on an object about 20 feet away.
- Put a dot on the left lens of your glasses, directly over the object.
- Without moving your head, open your right eye and close your left eye.
- Using your right eye, put a dot on the left lens of your glasses, directly over the object.
- With both eyes open, focus on the object and ensure the dots overlap into a single dot.
- Remove your glasses and measure (in mm) the distance between the two dots. This number represents your approximate pupillary distance.
- Re-measure three times to ensure accuracy.
#3 With the Help of a Friend
Having trouble measuring your pupillary distance on your own? Ask a friend to help! All they’ll need is a millimeter ruler.
- Stand about eight inches away from your friend, facing them with your eyes open.
- Stare straight ahead, focusing on an object about 20 feet away. Avoid looking at your friend while they’re measuring.
- Have your friend hold the ruler against your brow bone and line up the 0 mm mark with the center of one of your pupils.
- They should then measure to the center of the other pupil. This number represents your approximate pupillary distance.
- Have your friend re-measure three times to ensure accuracy.
#3 With a Pupillary Distance App
These days, there’s an app for pretty much everything, and measuring pupillary distance is no exception. The two highest-rated pupillary distance apps include:
- Glasses On: This app is the only medical-grade app for measuring PD and provides you with your measurement in less than a minute. All you’ll need to get your measurement is a standard magnetic card (i.e. library card). The app is available on Google Play or the Apple app store.
- Eye Measure: This app does not require additional tools like cards or measuring tapes and quickly provides your PD measurement.
Pretty cool, right? But are these apps accurate? The answer is yes! GlassesOn claims their PD measurement is accurate within 2 mm, and Eye Measure claims theirs is accurate within .50 mm.
As with the other methods, take your measurement three times to ensure accuracy.
How To Read Pupillary Distance on a Prescription
Do you already have a prescription from an optometrist? If so, pupillary distance is often included on your prescription, labeled as “PD.”
It will typically be one number. That is called a binocular PD, which can be used to order most prescription glasses.
If two different PD numbers are listed on your prescription, this is referred to as a monocular PD. The two numbers are measurements of the distances from the centers of each pupil to the center of the bridge of the nose.
Monocular PD is notated as 32/30, for example. The first number is the right eye measurement and the second is the left.
A monocular PD is often required when buying prescription multifocals, like progressives, but is usually unnecessary otherwise. If you only have a monocular PD, you can simply add the two numbers together to get your binocular PD.
Can Your Pupillary Distance Change Over Time?
Pupillary distance changes with physical development. As such, a growing child’s PD measurement will likely change over the years.
However, once a person reaches adulthood, very little change in skull shape occurs, causing the pupillary distance to remain constant. That means that if you’re an adult, you most likely only need to obtain an accurate pupillary distance once.
Finding Your Perfect Fit
Once you have an accurate PD measurement (as well as your other prescription details), now comes the fun part: choosing your perfect glasses!
Privé Revaux offers a wide selection of prescription glasses and readers that will help you see clearly and look great, too! You can browse our collection by lens size, lens type, style, color, and even face shape. Find your perfect fit today!