Pupillary Distance Measurement
Measure your pupillary distance (PD) for ordering glasses online with a webcam or a photo. Hold a standard card against your forehead for scale, mark the card edges and your pupils (or let the tool find them), and read your PD in millimeters, including the separate right and left measurements.
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Hold any standard-size card (bank card, library or loyalty card, 85.6 × 54 mm) flat against your forehead, long side level and centered above your eyes. Look straight into the camera from about an arm's length away. Cover any numbers on the card.
Line the card up with the dashed box and your eyes with the circles, keep your head level and look into the lens, then capture. The photo stays on your device.
Drag the markers, or pick one above and click where it belongs. Arrow keys nudge the selected marker by 1 pixel (Shift for 10). A magnifier appears while you drag.
Estimate only. A photo measurement is usually within a couple of millimeters when done carefully. For strong prescriptions, progressive or bifocal lenses, ask an optician to measure or confirm your PD.
How to use the Pupillary Distance Measurement
- Take or upload a photo: press Start webcam and Capture photo, or Upload photo. Hold a standard card flat against your forehead, long side level, and look straight into the lens from about 50 cm (20 in).
- Mark the card: drag the two orange markers onto the left and right edges of the card. Use the magnifier for precision.
- Mark the pupils: press Find pupils automatically, or drag the green markers onto the center of each pupil.
- Mark the nose bridge: place the purple marker on the middle of your nose between the eyes for dual PD.
- Read your PD: set the camera distance under Accuracy settings, then note the distance PD and the right and left values. Repeat with two or three photos and use the average.
How the PD is calculated
Scale: millimeters per pixel = card width (85.60 mm) ÷ card width in pixels.
Raw PD = distance between the pupil markers in pixels × millimeters per pixel.
Corrected distance PD = raw PD × (D + 10) ÷ D × 1 ÷ (1 − 10.5 ÷ (D + 20.5)), where D is the camera-to-card distance in mm, the card is assumed to sit 10 mm in front of the pupils, and 10.5 mm is the typical distance from the pupil to the eye's center of rotation. The first factor removes the card-depth effect and the second removes the inward turn of the eyes when looking at the camera.
Monocular PD: the nose bridge marker is projected onto the line between the pupils, and each side is measured from its pupil to that point, with the same corrections.
Near PD ≈ distance PD × (1 − 25.5 ÷ 425.5), for lenses about 25.5 mm in front of the eye's rotation center and a 40 cm reading distance.
How much the correction changes
| Camera to card | Correction factor | Raw 60.0 mm becomes | Raw 63.0 mm becomes |
|---|---|---|---|
| 30 cm (12 in) | × 1.068 | 64.1 mm | 67.3 mm |
| 40 cm (16 in) | × 1.051 | 63.1 mm | 66.2 mm |
| 50 cm (20 in) | × 1.041 | 62.5 mm | 65.6 mm |
| 70 cm (28 in) | × 1.029 | 61.8 mm | 64.8 mm |
| 100 cm (39 in) | × 1.020 | 61.2 mm | 64.3 mm |
Because the correction shrinks with distance, a photo taken from farther away (with a zoomed-in, high-resolution camera) depends less on the exact distance you enter.
Tips for an accurate measurement
- Use good, even light from the front so the pupils are clearly visible; take glasses off.
- Hold the card flat on your forehead, centered and level, touching the skin just above the eyebrows.
- Keep your head straight and look directly into the camera lens, not at the screen.
- Place the card markers exactly on the card's outer edges and the pupil markers on the pupil centers, using the magnifier.
- Repeat with two or three photos. If results differ by more than 2 mm, check head tilt and card position.
Frequently asked questions
What is pupillary distance?
Pupillary distance (PD) is the distance in millimeters between the centers of your pupils. Lens makers use it to put the optical center of each lens in front of each eye. Typical adult distance PDs are about 54 to 74 mm, and children's are smaller. A dual or monocular PD gives the distance from each pupil to the center of the nose separately, for example 31.5/32.0.
How does the card measurement work?
Bank cards, debit cards, most ID cards and many loyalty cards share the ISO/IEC 7810 ID-1 size of 85.60 × 53.98 mm. Because the card is in the photo at almost the same distance as your eyes, its width in pixels tells the tool how many pixels make one millimeter, and the pupil distance in pixels is converted with the same scale: PD = pupil distance (px) × 85.60 ÷ card width (px).
Why are corrections applied?
Two small effects make a raw photo measurement read low. The card on your forehead is about 1 cm closer to the camera than your pupils, so it looks slightly larger; and your eyes turn inward a little to look at a camera 50 cm away. With the default 50 cm camera distance the correction adds about 4%, for example a raw 61.6 mm becomes about 64.2 mm. You can turn the correction off or enter your actual distance under Accuracy settings.
What is the difference between distance PD and near PD?
Distance PD is measured with the eyes looking far away and is used for everyday and distance glasses. When you read, your eyes converge, so the PD at the lenses is smaller, usually about 3 to 4 mm less. The tool estimates near PD for a 40 cm reading distance; use it only for single-vision reading glasses.
How accurate is an online PD measurement?
With a sharp, straight-on photo, a level card and carefully placed markers, results are typically within about 1 to 2 mm of an optician's measurement. Errors come from tilting the head, not holding the card flat, looking away from the lens and low-resolution photos. Measure two or three times and average the results; for progressive, bifocal or high prescription lenses, have an optician confirm it.
Is my photo uploaded anywhere?
No. The webcam image and any photo you choose are processed only in your browser on your device. Nothing is sent to a server, and the photo is gone when you close the page.
Can I use a card other than a bank card?
Yes, as long as you know its exact width. Measure the long side with a ruler in millimeters and enter it in Card width under Accuracy settings. Library cards, gift cards and gym cards are very often the standard 85.60 mm. Cover the numbers on any payment card before taking the photo.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.