How PD measurement works
Pupillary distance (PD) is the space between your pupils in millimeters. Online glasses need it so lenses sit correctly in front of your eyes.
Why a credit card?
Webcams don’t know real-world size. A standard ISO credit card is always 85.60 mm wide. Holding one near your face gives the app a ruler: once you mark the card’s left and right edges, every pixel maps to millimeters.
What the app measures
- Binocular PD — distance between left and right pupil centers (most common for single-vision glasses).
- Monocular PD — each eye to the bridge of the nose (useful for progressive lenses).
Tips for a better reading
- Sit about an arm’s length from the camera in even lighting.
- Look straight at the lens; keep your head level.
- Hold the card flat across your mouth at the same distance as your face (not pushed toward the camera).
- Wait for the cyan box to lock onto the card edges—the app tracks it automatically.
- Take 2–3 captures and use the average if results vary slightly.