Online Eye Test

A calibrated visual-acuity check: size a bank card on screen for true pixels-per-mm, set your distance, then read tumbling-E charts at the correct physical size for an approximate 20/20 result.

Step 1 · Calibrate your screen

Hold any bank, credit or ID card flat against the screen and drag the slider until the box is exactly the card's width. Every such card is 85.6 mm wide worldwide, so this gives your display's true size.

Match this box to a real card · —
cm —
Sit this far from the screen for the test. About 1–2 m works well; further is more precise but needs a bigger screen. Use a tape measure if you can.

Wear your usual glasses or contacts if you want to test your corrected vision.

Why this eye test is actually calibrated

Most "online eye tests" show letters at a random pixel size, so the result is meaningless — a letter that fills the chart on a phone is tiny on a 4K monitor. The only way to make it real is to know the physical size of what's on screen. This tool gets that from a trick opticians' apps use: every bank, credit and ID card follows the ISO/IEC 7810 ID‑1 standard and is exactly 85.60 mm wide. Match a card to the on‑screen box and we know your display's true pixels‑per‑millimetre.

With that plus your viewing distance, each tumbling‑E is drawn so its strokes and gaps subtend the right angle: a 20/20 letter spans 5 arc‑minutes, with each of its five elements at 1 arc‑minute — exactly how a printed Snellen chart is defined. You report which way the E points; we step the size down line by line and report the smallest you can reliably read.

Screening only. A clinic test controls lighting, exact distance and chart contrast, and an eye exam checks far more than acuity. Use this as a quick check or to track changes — not as a diagnosis. Everything runs in your browser; nothing is uploaded.

How to get the best reading

Calibrate carefully with a real card, measure your distance with a tape if you can, test in a well‑lit room (no glare on the screen), and cover — don't squint — the eye you're not testing. Test each eye on its own; small differences between eyes are normal, but a big gap is worth mentioning to a professional.

Frequently asked questions

How can an online eye test be accurate?

By calibrating to physical size. Matching a fixed‑width bank card gives true pixels‑per‑mm, and with your distance the letters are drawn at the exact angle a real chart uses. It's a screening, not a clinical exam.

Is this a substitute for a real eye exam?

No. It checks distance acuity only — not eye health, prescription or pressure. See an optometrist or ophthalmologist for a proper exam.

What is the tumbling E?

A letter E rotated to point up, down, left or right. You report the direction of the three prongs. It needs no reading ability, so it works in any language and for kids.

What does 20/20 mean?

At 20 feet you see what a typical eye sees at 20 feet. 20/40 means somewhat reduced vision: you need to be at 20 feet to read what a typical eye reads at 40.

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