What is PD (pupillary distance)?
How to measure PD correctly
Understand PD so lenses are centered — clear vision, less eye strain. Free AI PD measurement in your browser.
Many people think an eye test is only about sphere power. When lenses are made, the lab also needs PD (pupillary distance) to center the lenses — for clear, comfortable vision and less fatigue.
What is PD? Single vs dual PD
PD (Pupillary Distance) is the distance between your pupils in millimeters. It is required to align the optical center of the lenses with where you actually look.
Single PD (binocular)
Distance from one pupil center to the other. Example: 62 mm.
Dual PD (monocular)
Distance from the nose bridge to each pupil. Example: 30 / 32 mm (OD/OS).
Adults usually fall around 54–74 mm. Children’s PD changes with age.
Why measure PD?
PD sets where the optical center of the lens sits. If it is off, you can still have problems even when power is correct:
- Eye strain or dizziness after long wear
- Blur or distortion toward the edge
- Faster progression (especially in children)
- Discomfort with progressive lenses
How to read PD on a prescription
Single PD (OU)
62 mm for both eyes together.
Dual PD
30 mm right eye (OD), 32 mm left eye (OS).
How to measure PD correctly
In store (most accurate)
Staff use an autorefractor or a dedicated PD meter. At Dien Bien Phu Eyewear, PD is part of our standard refraction workflow.
At home with a mm ruler
Use a mm ruler and a mirror (or a helper). Align zero with one pupil center and read the value at the other. Measure 2–3 times and average.
- Look straight ahead; keep your head still.
- Near PD is often 2–3 mm smaller than distance PD.
Online PD with AI (free)
Far from the shop or lost your slip? Dien Bien Phu Eyewear offers a browser tool using your camera and AI — no photo upload, results in seconds.
- Open pd.kinhmatdienbienphu.com, tap Start PD, and allow the camera.
- Center your face, look straight, keep steady (glasses off is best).
- The app shows PD in mm; you can save or share the result.
Use good lighting, 30–70 cm from the camera. Result is indicative; in-store measurement is best for progressives or bifocals.
Where should I measure PD?
A hospital or reputable optical shop reduces decentered lenses. Dien Bien Phu Eyewear at 529 3/2, Ward Vuon Lai, HCMC — refraction and PD by trained staff with French/Japanese-standard equipment. In-store eye tests are free.
FAQ
Free PD — on phone or desktop
Camera + AI, no photo stored. Results in seconds for ordering lenses.
Open PD tool529 3/2, Ward Vuon Lai, HCMC — free in-store eye test