Measure Your Pupillary Distance

Pupillary distance is the distance between the centres of your two pupils, measured in millimetres. Glasses lenses are centred on your pupils, so an online glasses store needs your PD to make lenses that line up with your eyes.

It needs a known size in the photo. A bank card is exactly 85.6 mm wide worldwide, so the tool compares the pixel distance between your pupils to the pixel width of the card and converts it to millimetres.

With a straight-on selfie and the card flat on your forehead, it gives a reliable estimate — usually within a millimetre or two — which is fine for ordering single-vision glasses. For progressive lenses or the most exact result, have an optician measure your PD.

Most adults have a PD between 54 and 74 mm, with around 63 mm being typical. Children's PD is smaller. The tool warns you if a reading falls outside the usual adult range.

This tool measures your total (binocular) PD, which most stores accept for everyday single-vision glasses. Some prescriptions use monocular PD — the distance from each pupil to the bridge of the nose — which an optician can provide.