Measure your pupillary distance online.

Hold a standard bank card flat against your forehead, just below your eyes, and let your camera find your irises against the card's known width for scale. It takes about 30 seconds on a phone or laptop, and nothing is uploaded — the measurement runs entirely in your browser.

Adult PD usually falls between 54 and 74 mm, with most people close to 63 mm. Men run slightly higher than women on average. There is no ideal number — it simply describes the distance between your pupils, and lenses are centered to match yours specifically.

Often not. Opticians measure it in seconds at the counter but frequently leave it off the printed paper, since a missing PD sends you back to the shop that already has your frames. Online lens retailers require it separately, which is why a self-measurement tool exists.

Distance PD is measured looking far away and is the number used for regular glasses. Near PD, used for reading glasses, is about 3 mm smaller because your eyes turn slightly inward when focusing up close. Most online retailers calculate near PD for you automatically.

About plus or minus 0.5 to 1 mm on a laptop camera, and 1 to 1.5 mm on a phone, depending on how carefully the card edges line up with your forehead. Online lens shops round to the nearest millimeter anyway, so this accuracy is within their tolerance.

A single PD is fine for most orders and is simply split evenly between your eyes. Some order forms ask for two numbers, one per eye, which is more precise if your face is noticeably asymmetric. Either version works for standard lens centering.