Pupillary Distance Calculator – Measure PD From a Photo

Measure your pupillary distance from a photo

Your pupillary distance (PD) is the distance between the centres of your pupils, in millimetres. Glasses shops ask for it so the optical centre of each lens sits in front of each eye. This pupillary distance calculator measures it from a photo: hold any credit-card-sized card against your forehead, take a picture looking into the camera, and mark the card edges and your pupils. Because every bank card is the same width, the card turns pixels into millimetres.

You get the single PD, the dual (monocular) PD for each eye if you mark the nose bridge, and an estimated near PD for reading glasses. It works like a pupillary distance app without installing anything: the photo never leaves your browser and the page never opens your camera.

How to use the Pupillary Distance Calculator

1. Hold a bank, ID or store card flat on your forehead just above the eyebrows, the long side level.
2. Look straight into the camera at about arm’s length and take a sharp, well-lit photo with your face square to the lens.
3. Choose the photo. Click the middle of the card’s left short edge, then its right short edge.
4. Click the centre of each pupil, then (optional) the middle of your nose bridge for dual PD. Drag any marker, or use the arrow buttons, to fine-tune — a magnifier appears while you drag.
5. Set the camera distance and keep “I was looking into the camera” ticked if you were. Read your PD and copy it.

Pupillary Distance Calculator features

How the PD is calculated

Scale: the card’s short edges are 85.60 mm apart, so pixels per mm = card pixels ÷ 85.60, and PD = pupil pixels ÷ pixels per mm. Worked example (the sample photo): the card spans 299.6 px, or 3.5 px per mm; the pupils are 220.5 px apart, so the uncorrected PD is 220.5 ÷ 3.5 = 63.0 mm.

Gaze: glasses are fitted for eyes looking into the distance, but in a selfie your eyes converge on the lens. Each eye turns about its centre of rotation, roughly 13.5 mm behind the cornea, and the pupil sits about 3 mm behind the cornea, so it swings inward on a radius of about 10.5 mm. With the camera 50 cm away each pupil moves in by about 0.65 mm; correcting for it turns the sample’s 63.0 mm into 64.3 mm. Untick the box if you were looking into the distance past the camera.

Depth: the card sits slightly in front of your eyes, so the eyes look a little smaller than the card. Enter an allowance in “Pupils behind the card” if you want to include it — 10 mm at 50 cm adds 2%.

Typical PD values and near PD

In Dodgson’s 2004 review of anthropometric data, the mean adult PD is about 63 mm, and the large majority of adults fall between about 50 and 75 mm; children’s PDs are smaller. A result far outside that range usually means a point is in the wrong place.

For reading glasses the eyes converge, so the near PD is smaller. The calculator uses PD × 400 ÷ (400 + 27) for a 40 cm reading distance, about 3–4 mm less than the distance PD — the usual rule opticians quote.

No photo? The mirror-and-ruler method

A pupillary distance ruler works too: stand 20 cm from a mirror, hold a millimetre ruler under your eyes, close your right eye and line the zero up with the centre of your left pupil, then close your left eye and read the mark under your right pupil. Print a true-scale ruler with the printable ruler or calibrate an on-screen one with a card using the online ruler (the ring size chart uses the same card trick). Repeat three times and average.