Near PD for Reading Glasses: What It Is and How to Calculate It

If you are ordering reading glasses, you may come across a measurement called "near PD" — and find that it is a slightly different number from the PD you use for distance glasses. This is not an error. Near PD is genuinely smaller, for a simple anatomical reason, and this article explains what it is, how to work it out from your distance PD, and when the difference actually matters.

For the basics of pupillary distance and how to measure it, see our complete guide to measuring pupillary distance.

Why near PD is smaller than distance PD

Your eyes do not stay pointed straight ahead. When you look at something close — a book, a phone, a screen at arm's length — both eyes rotate slightly inward to focus on it. This inward turn is called convergence, and it is completely normal; it is how you keep a near object as a single, clear image.

Because your eyes converge for near vision, the effective distance between your pupils is a little smaller when you are reading than when you are looking at the horizon. Reading glasses are made for that converged position, so they use a near PD that reflects it. Distance glasses, made for when your eyes look straight ahead, use your full distance PD.

How to calculate your near PD

The standard rule of thumb is straightforward: subtract 3 mm from your distance PD to get your near PD.

So if your distance PD is 63 mm, your near PD is about 60 mm. If your distance PD is 58 mm, your near PD is about 55 mm. The 3 mm accounts for the typical amount of convergence at normal reading distance.

If you use a dual PD — a separate number for each eye — subtract 1.5 mm from each side instead. A distance dual PD of 31.5 / 31.5 becomes a near dual PD of about 30 / 30.

This rule is an approximation, but it is the one the industry uses, and it is accurate enough for ordinary reading glasses.

When the difference matters — and when it doesn't

Whether you need to worry about near PD depends on what you are ordering.

For dedicated reading glasses — single-vision lenses you wear only for close work — using the near PD gives you the best centered vision for reading. It is the right number for the job.

For ordinary distance glasses, you use your distance PD, full stop. There is no need to adjust it.

For progressive lenses, you generally provide your distance PD, and the lens design itself accounts for convergence in the near-vision zone of the lens. You usually do not subtract anything yourself for progressives — but because progressives are precision lenses, it is worth following the specific instructions of whoever is making them.

A note on accuracy

The 3 mm rule assumes a typical reading distance and average eye anatomy, so it is a sensible default rather than a personalized measurement. For most people ordering reading glasses, it works well. If you have a strong prescription, do very close detailed work, or want the most precise result, an optician can measure your near PD directly for your specific reading distance.

The bottom line

Near PD is your pupillary distance for close-up vision, and it is smaller than your distance PD because your eyes converge inward when you read. To find it, subtract 3 mm from your distance PD (or 1.5 mm from each side of a dual PD). Use near PD for dedicated reading glasses, use your distance PD for distance glasses, and follow the maker's instructions for progressives. The rule is an approximation, but a reliable one for everyday reading glasses.

This article is for general informational purposes and is not medical advice. For strong prescriptions or precise near-vision needs, consult an optician or eye care professional.