When you order glasses online, you will usually need to provide your pupillary distance, or PD. This measurement tells the lab where to position the optical center of each lens so that it aligns with your pupils. Get it wrong, and your glasses may feel uncomfortable, cause eye strain, or even give you headaches – even if your prescription is perfect.
Many people feel intimidated by the idea of measuring their own PD, but it is actually a straightforward process that takes just a few minutes. In this guide, we will explain what PD is, why it matters, and how to measure it accurately at home using simple tools you already have.
Your pupillary distance is the measurement, in millimeters, between the centers of your pupils. For most adults, this number falls somewhere between 54 mm and 74 mm, with an average around 63 mm. Some people have slightly different measurements for each eye, which is called a dual PD (for example, 31/32 mm instead of a single 63 mm).
PD is crucial because prescription lenses are designed to bend light in a specific way, and that bending needs to happen directly in front of your pupils. If the optical centers of the lenses do not line up with your eyes, you end up looking through the wrong part of the lens, which can cause:
This is why PD is just as important as your prescription strength when ordering glasses.
Some people are surprised to discover that their PD is not always included on their prescription. Technically, a glasses prescription only has to include sphere, cylinder, axis, and add power (for multifocals). PD is considered a fitting measurement, not a prescription measurement.
Many eye doctors will measure your PD during your exam and provide it if you ask. However, some offices are reluctant to share it, especially if they suspect you plan to order glasses online instead of buying from them. If your doctor will not give you your PD, do not worry – you can measure it yourself at home with good accuracy.
You do not need any special equipment. Here is what to gather: