What pupillary distance is and why it matters

Pupillary distance is the horizontal gap between the centers of your two pupils, measured in millimeters. Prescription lenses have an optical center that must line up with your pupils — if the PD is wrong, you get eye strain, headaches, or blur, especially in stronger prescriptions. It is the one measurement your prescription usually does not include, so you often have to supply it yourself when ordering online.

PD ruler FAQ

What is a normal PD?

Most adults fall between 54 and 74 mm, and the average is about 63 mm. Women average slightly narrower than men, but the range overlaps heavily — measure yours rather than assuming.

Single PD vs dual PD — what is the difference?

A single PD is the total distance pupil to pupil. A dual PD splits it into two numbers — the distance from each pupil to the center of your nose — which is more precise for progressive and high-power lenses. If you are given two numbers, they add up to your single PD.

How accurate does my PD need to be?

Within about 1 mm is fine for most single-vision lenses; progressive and strong prescriptions want it as exact as possible. Measure twice, and if the two readings differ, take a third.

Can an optician measure it for me?

Yes, in seconds, and it is worth asking at your next eye test — book one from the header if you are due. For ordering online in the meantime, this ruler gets you a reliable number.

Last updated: July 21, 2026 · Glasses Atlas Team · More free tools