The PD Journal
How to Measure Your PD With a Phone Camera: Setup, Distance and Light
Last updated: October 2026 | Reading time: 8 minutes
Short answer: use the front camera, hold the phone at arm's length with the lens at eye level, look into the lens, and put a bank card flat on your forehead as the scale. Good light and a level head matter more than the phone model.
Open the free PD tool on your phone, or take a photo first and upload it.
Why phone photos are tricky
A phone is a wide-angle camera. Wide lenses stretch things near the edges and make close objects look larger relative to distant ones. For a PD measurement that creates three problems:
- Perspective. Your forehead is closer to the lens than your pupils. A card on your forehead looks slightly bigger than it would at pupil depth.
- Distortion. Features away from the image centre are stretched. Keep your face in the middle of the frame.
- Angle. If the phone is held above or below eye level, the vertical tilt distorts your face.
Good technique reduces all three. The tool also applies corrections for the card-to-pupil depth difference, but it cannot undo a bad photo.
Setup that gives the cleanest result
Distance
Hold the phone about an arm's length away, roughly 35 to 50 cm. Too close increases perspective effects and makes your eyes turn inward more; too far makes your eyes small in the frame, so each pixel of error counts for more millimetres.
Height and angle
Lens at eye level, screen vertical, no tilt. Rest your elbows on a table or lean the phone against a stack of books if your arms shake. A steady phone gives a sharper photo.
Light
- Face a window or a lamp, so the light falls evenly on your face.
- Avoid a bright light directly behind you: the camera lowers exposure and your face gets dark.
- Avoid a light directly in front that reflects off your pupils. Glare can hide the pupil edge.
Background
A plain wall is best. A busy background does not matter for the pupils, but a card that matches the wall colour is harder to detect.
Your face
- Glasses off if possible.
- Keep both eyes fully open. Look into the lens, not at the screen.
- Relax your forehead: lifting your eyebrows moves the card and changes its position relative to your eyes.
Camera or upload?
The tool offers both. Live camera gives guidance as you aim. Upload lets you use a photo you took with your phone's normal camera app, which often has higher resolution. If you upload, keep the card fully visible, the face frontal, and the image uncropped and unmirrored-edited: do not apply filters or beauty modes, because they change facial geometry.
Common phone problems
| Symptom | Likely cause | Fix |
|---|---|---|
| Card not found | Low contrast with the wall | Use a darker card or a different wall |
| "Head turned" message | Phone held to the side | Centre your face in the frame |
| Values differ between shots | Moving between shots | Rest your elbows; take 3 shots |
| Eyes look small | Phone too far away | Move to about 40 cm |
| Strange result with a selfie filter on | Beauty mode alters geometry | Turn all filters off |
Is a phone good enough?
For basic single-vision glasses, phone-based measurement can be a reasonable estimate. It is not a substitute for an optician's measurement for progressive lenses, strong prescriptions, or children's glasses. If a number looks wrong, check it against the typical adult range in is my PD normal? and retake the photo.
Related guides
- How to measure your PD with a credit card
- PD tool not working: fixes for common errors
- Online PD apps: how accurate are they?
- How to measure PD at home
Sources and further reading
- MediaPipe Iris, Google Research, on iris landmark tracking from a single camera.
- Comparing the effectiveness of smartphone applications in the measurement of interpupillary distance (PMC10389117), a published comparison of smartphone PD apps against a digital pupilometer.