Pupillary Distance (PD) Calculator
Convert between per-eye and both-eyes PD, and estimate the near PD your reading glasses need — the measurement that centres every lens on your eyes.
Your pupillary distance
The near PD is smaller than the distance PD because your eyes turn inward to focus up close. Reading glasses and the near zone of progressives are centred on it.
The one number that centres your lenses
Every lens has an optical centre — the point where it bends light the least. For comfortable vision that centre needs to sit in front of your pupil. Your pupillary distance is how the lab knows where to put it. In weak prescriptions a millimetre or two rarely shows, but as power climbs, an off-centre lens starts to act like a small prism, pulling your eyes and causing headaches and fatigue.
Distance PD is measured with your eyes relaxed on something far away; near PD applies when you converge on a book or screen. Single-vision distance glasses use the distance PD, dedicated readers use the near PD, and progressives use both. This tool moves between all of them so you can order — or sanity-check a dispensed pair — with the right figure.
Frequently Asked Questions
What is pupillary distance and why does it matter?
Pupillary distance (PD) is the distance in millimetres between the centres of your pupils. It tells the lab where to place the optical centre of each lens so it lines up with each eye. Get it wrong and you can end up looking through the lens off-centre, which causes eye strain, especially in stronger prescriptions.
What's the difference between binocular and monocular PD?
Binocular PD is a single number for both eyes together — pupil to pupil. Monocular PD is measured separately for each eye, from the centre of the nose to each pupil, because faces are rarely perfectly symmetric. Two monocular values simply add up to the binocular total; this tool converts either way.
Why is my near PD smaller than my distance PD?
When you look at something close, your eyes rotate inward (converge), so the pupils move closer together. The near PD is therefore a few millimetres smaller than the distance PD. Reading glasses and the near zone of progressive lenses are centred on this smaller value. The tool scales distance PD by the reading distance to estimate it.
What is a normal PD?
Most adults fall between about 54 and 74 mm, with 60–65 mm common. Children's are smaller. There's no single 'right' number — it's simply your anatomy — so what matters is measuring it accurately rather than comparing it to an average.
Can I rely on a PD I measured at home?
A careful home measurement with a millimetre ruler or a printed PD gauge is fine for browsing and for many single-vision online orders. For strong prescriptions, progressives, or if you notice strain, have it measured by an optician — small errors matter more as power increases.
Educational estimate. For a dispensed pair — especially strong prescriptions or progressives — have your PD measured by an optician.