Pupillary Distance (PD) Calculator
Turn a distance pupillary distance into near PD and single (monocular) PD values for ordering glasses online.
How it works
Near PD ≈ distance PD − 3 mm · Single (monocular) PD ≈ distance PD ÷ 2
Pupillary distance is the gap between the centres of your two pupils, and it tells the lab where to place the optical centre of each lens. Because your eyes converge slightly when you look at something close, the near PD used for reading glasses is a few millimetres smaller than the distance PD. Some online retailers ask for a single (monocular) PD per eye, which is simply roughly half of the binocular value — though a true monocular measurement can differ between eyes.
Worked example
With a distance PD of 63 mm: near PD is 63 − 3 = 60 mm, and the single PD is 63 ÷ 2 = 31.5 mm per eye. You would enter 63 for distance glasses or 60 for dedicated readers.
Frequently asked questions
Why is near PD smaller than distance PD?
Your eyes rotate inward (converge) when focusing on close objects, so the pupils move slightly closer together. The typical adjustment is about 3 mm, which is why reading-glasses PD is smaller.
What is a normal PD?
Most adults fall between 54 and 74 mm, with an average around 62–64 mm. Children are smaller. It is a physical measurement, not a health indicator.
Can I measure PD myself?
You can estimate it with a millimetre ruler and a mirror, but a small error shifts the optical centres. For strong prescriptions especially, have an optician measure it.
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Educational estimate only, not medical advice — talk to an eye doctor, dentist, dermatologist or other qualified professional about your own care.