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How to Measure Pupillary Distance (PD)

Reviewed by : Dr. Matthew Miller, OD on May 19th, 2022

You'll need to know your PD if you want to order eyeglasses from EyeBuyDirect. Don't worry if your glasses prescription doesn't include your PD, we can show you how to measure it by yourself.

How to measure your pd

PD, or pupillary distance, refers to the distance in millimeters between the center of one pupil to the center of the other. Having a correct PD on your glasses prescription ensures that you are looking through the ideal spot in your lenses. If this number was not provided on your prescription by your eye care professional, you can measure it yourself.

Measure PD yourself

1
Print our downloadable PD ruler
2
Place the ruler directly over the center of your right pupil so that the ruler is horizontal. Place against forehead for added stability. Stand in front of a mirror, or ask someone else to measure for you.
3
While looking straight ahead, measure the distance from the center of your right pupil to the center of your left pupil.
4
Repeat a couple of times for accuracy and use an average for your final measurement.
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FAQ

👀What is ‘pupillary distance’?

Your pupillary distance (PD) is the distance between the centers of your pupils. Your PD is an important part of your prescription because it shows exactly which part of the lens you look through.

📏How do I measure my PD without a ruler?

There are various mobile apps that can measure your PD using your phone’s camera. You can find EyeBuyDirect’s PD measurement tool by pressing the ‘i’ button in the PD section when entering your prescription.

👓Can I find my PD on my glasses?

You usually can’t find your PD number written on your eyeglasses. The numbers on the inside of the temple arms of some frames show the measurements for the frame itself. Your PD number should be written on your eyeglass prescription in the PD section.

📐Does my PD have to be exact?

Your PD should be exact. If your lenses aren’t centered correctly, they can cause discomfort and eye strain. A small margin of error might not cause problems, but it’s better to be as accurate as possible.

📝Where is my PD on my prescription?

Your PD number will be in the ‘PD’ or ‘pupillary distance’ section of your eyeglass prescription. This is often separate from the ‘grid’ section of your prescription - where the doctor writes out the main prescription information.

😣What happens if my pupillary distance measurement is off?

If your eyeglass lenses aren’t properly centered based on your PD number they can cause dizziness, headaches or blurred vision. Your vision is centered on a small section of the lenses, so a PD number is needed to shape the lenses to perfectly suit your needs.

👓Does PD affect frame size?

Your PD has no effect on the size of your eyeglass frame. The PD number influences the shape of your lenses, but not the frame.

🤔Does PD change over time?

A person’s pupillary distance will change when they are young as they are still physically growing. Once we reach maturity and stop growing, our pupillary distance will change very little, if at all.

👓Is PD important for single vision glasses?

The PD number indicates exactly which part of the lens you look through; therefore, the PD number is important for every type of prescription lens, including single vision glasses.

👀What is the difference between ‘single’ and ‘dual’ pupillary distance?

A ‘single’ pupillary distance number is the distance in millimeters between one eye’s pupil to the other eye’s pupil. A ‘dual’ pupillary distance number is the distance in millimeters from each eye’s pupil to the center of your nose. A single PD will be just one number, while a dual PD will have a number for each eye, marked ‘right’ and ‘left’. (Some prescriptions may have ‘OD’ for the ‘right’ eye, and ‘OS’ for ‘left’ eye.)