Near PD for Reading Glasses: What It Is & How to Get It

What is near PD?

Near PD is the pupillary distance measured when your eyes are focused on something close, such as a book or phone. When you look at a near object, both eyes rotate inward — a movement called convergence — so the centers of your pupils sit closer together than they do when you stare across a room. That smaller measurement is your reading PD.

Because of this inward rotation, near PD is always a little smaller than your distance PD. For a standard reading distance (roughly 40 cm), the difference is typically about 3 mm, and commonly falls in the 3–4 mm range. Your distance PD is the value used for glasses you wear to see far away; your near PD is the value used for dedicated reading glasses.

Why near PD is smaller than distance PD

When you focus on a distant object, your lines of sight are essentially parallel, so your pupils are at their widest spacing. As the object moves closer, your eyes converge to keep it in focus, and the pupils drift toward your nose. The closer the object and the further apart your eyes start, the larger this shift becomes — which is why distance PD vs near PD is a meaningful distinction for any close-work lens.

When do you actually need near PD?

You need a near PD mainly for dedicated single-vision reading glasses. These lenses are optically centered for close work, so aligning them to your reading PD keeps the optical center in front of each pupil and avoids eye strain.

For progressive or bifocal lenses, the situation is different. The lab usually starts from your distance PD and applies a built-in near inset for the reading portion, so you would normally supply your distance PD — not a separate near figure. If a retailer asks only for a single PD number, that is almost always the distance value. It's worth measuring both so you always have the right one to hand; see our guide on dual PD and monocular PD for the per-eye breakdown.

How to estimate near PD from distance PD

The simplest way to get a near PD is to measure your distance PD and subtract about 3 mm. If you haven't measured yet, our guide to measuring pupillary distance walks through every method, and you can also check how your number compares against the average pupillary distance.

1. Measure your distance PD (in millimeters).
2. Subtract roughly 3 mm to estimate your near PD.
3. Use the near value when ordering single-vision reading glasses.

Our tool does this for you automatically: when you measure your PD, it reports your distance PD and computes an estimated near PD at the same time, so you don't have to do the math by hand.

Worked example

Suppose your distance PD comes out to 63 mm. Subtract about 3 mm and your estimated near PD is roughly 60 mm. So you'd order distance glasses with a PD of 63 mm and single-vision reading glasses with a near PD of about 60 mm.

A quick word of caution

The 3 mm rule of thumb works well for typical reading distances and prescriptions. If you have a strong reading prescription, a large PD, or an unusual working distance — for example, a music stand, a workbench, or a computer monitor that sits further away than a book — the ideal near PD can differ. In those cases, confirm the figure with an optician so your lenses are centered correctly.