What Is Pupillary Distance (PD)?

Pupillary distance meaning

Pupillary distance (PD) is the distance, measured in millimetres, between the centres of your two pupils. It tells an optical lab exactly where you look through your lenses, so every pair of glasses can be built around your eyes rather than an average. When people ask what is pupillary distance, the short answer is simple: it's a single small measurement, but it has an outsized effect on how comfortable your glasses feel.

PD is usually written as one number for both eyes together (for example, 63 mm), or as two numbers when each eye is measured separately from the centre of the nose.

Why pupillary distance matters for glasses

Every lens has an optical centre — the point designed to give you the clearest, most relaxed vision. Your PD tells the lab where to place that optical centre so it sits directly in front of each pupil. Get it right and your eyes look through the sweet spot of the lens. Get it wrong and the optical centre is shifted sideways, forcing your eyes to compensate.

An inaccurate PD is one of the most common reasons new glasses feel "off." Symptoms can include eye strain, headaches, blurred or doubled vision, and a sense that the prescription is wrong even when it isn't. The stronger your prescription, the more a small PD error matters — which is why getting your pupillary distance for glasses correct is worth the few minutes it takes.

Binocular (single) PD vs monocular (dual) PD

A binocular or single PD is the total distance between both pupils — the everyday number most people use. A monocular or dual PD measures each eye separately, from the centre of the bridge of the nose to each pupil (for example, 31.5 / 31.0). Dual PD is more precise because few faces are perfectly symmetrical, and it's especially useful for progressive and high-power lenses. Learn more in our guide to dual PD vs monocular PD.

Distance PD vs near PD

Your eyes turn slightly inward when you focus on something close, so the gap between your pupils shrinks a little. Distance PD is measured while looking far away and is used for everyday and distance glasses. Near PD is usually about 3 mm smaller and is used for dedicated reading glasses. If you're ordering readers, see our note on near PD for reading glasses.

Typical pupillary distance values

Most adults have a PD between roughly 54 mm and 74 mm, with an average of about 63 mm. Women tend to sit slightly below that average and men slightly above, while children's PDs are smaller and grow with the face. There's no "good" or "bad" PD — it's simply a fixed feature of your anatomy. For a fuller breakdown by age and gender, see average pupillary distance.

How is pupillary distance measured?

PD is measured by lining a millimetre ruler up with your pupils, or by using a photo or camera-based tool that detects your pupils and a reference object of known size. You can do it yourself in front of a mirror, or have a friend help for a steadier reading. Our step-by-step how to measure pupillary distance guide walks through each method, and you can use the free PD measuring tool to get a number in under a minute — nothing is uploaded.

PD is often missing from your prescription

Here's something many people don't realise: your eyeglass prescription frequently doesn't include your PD at all. Pupillary distance is technically a fitting measurement rather than part of the refraction, so some opticians leave it off — and a few are reluctant to hand it over when you plan to buy glasses elsewhere. We cover the reasons in why opticians won't give your PD.

The good news is that you don't need anyone's permission. PD is your own measurement, it's easy to take accurately at home, and once you have it you can order glasses online with confidence. Start with the free, private PD tool or read the full measuring guide first.