How to Get Your Pupillary Distance (PD) for Glasses Online
What PD is, why it's often missing from your prescription, the most accurate ways to get it, and when an exact number matters most.
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Pupillary distance (PD) is the distance between the centers of your pupils, in millimeters. Online glasses stores need it to line up the optical center of each lens with your eyes. If your prescription doesn’t show it, you’re not alone – and there are easy ways to get it.
This guide is general information, not medical advice. For the most accurate measurement, ask your eye doctor or an optician.
Why PD is often missing
According to the FTC, only a few US states require eye doctors to include PD on a glasses prescription; most don’t, and in some states they can charge to measure it. If you were measured but not given the number, you may be able to request it from your records.
How accurate does it need to be?
The American Academy of Ophthalmology says PD can be measured very precisely, and how much an error matters depends on your lenses:
- Progressives and high-power lenses: even a small PD error can cause problems.
- Low-power single-vision glasses: more forgiving – a larger error may cause no symptoms.
Symptoms of glasses that are off can include headaches or discomfort; if new glasses feel wrong, check your PD and prescription with an eye care professional.
Ways to get your PD (most to least accurate)
- Ask your eye doctor or optician. Call the office where you had your exam and ask whether they recorded it. An optician can also measure it quickly.
- Use the store’s measuring tool. Most online glasses retailers offer a camera-based or guided measurement during checkout.
- Measure with a ruler and a mirror or a friend. Hold a millimeter ruler under your eyes and measure from the center of one pupil to the center of the other while looking straight ahead at a distant point. Repeat a few times and use the average.
Single PD vs dual PD
- Single PD is one number for both eyes (e.g., 63).
- Dual PD is two numbers, one per eye measured from the bridge of your nose (e.g., 31.5/31.5). If your prescription gives two numbers, enter both – it’s more precise, especially for progressives.
Before you order
- Double-check right (OD) and left (OS) values – see how to read your glasses prescription.
- Use a store with a generous return window in case the fit is off. GlassesUSA gives 60 days for a full refund; see our best places to buy glasses online.