Online Tool Store
Eye Test Chart
Calibrate your screen with a bank card, pick any viewing distance, and read a Snellen chart drawn at its true physical size. Results per eye.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Step 1 — Calibrate your screen
Not calibratedHold any bank or ID card flat against the screen and drag the slider until the outline matches it exactly. Bank and ID cards are 85.60 × 53.98 mm under ISO/IEC 7810 ID-1, so matching either edge tells the chart how big a millimetre is on your display. On a phone the long edge is usually wider than the screen — match the short edge instead.
Step 2 — Set your distance
Step 3 — Record what you read
Click the smallest row you can read correctly without squinting. Results are kept on this page only.
This is an informal screening aid, not a medical device and not a diagnosis. Screen quality, lighting, and how accurately you measure your distance all affect the result. See an optometrist or ophthalmologist for a real eye examination, and seek urgent care for any sudden change in vision.
How the eye test chart works
- Calibrate once: hold a bank or ID card against the screen and drag the slider until the outline matches it. The chart now knows how big a millimetre is on your display.
- Choose the viewing distance you can actually manage, in metres or feet. Every row is redrawn for that distance.
- Pick both eyes, or one eye at a time and cover the other with your palm. Each switch deals a fresh set of letters so the second eye is not reading from memory.
- Step back to the distance you selected and read down the chart. Use fullscreen if the largest rows are crowded.
- Click the smallest row you can read cleanly. It is recorded per eye and shown in 20/x, 6/x, decimal, and logMAR notation.
The method
A Snellen optotype is defined by the angle it subtends at the eye: the whole letter spans five arcminutes at its reference distance, and the strokes and gaps that tell one letter from another span one arcminute. Letter height therefore follows w = 2 × d × tan(θ / 2), where d is your viewing distance and θ is five arcminutes scaled by the row's denominator. At exactly 6 m that yields 8.73 mm for the 6/6 row and 87.3 mm for the top 6/60 letter - the published dimensions of a physical chart, which is how you can tell the on-screen version is sized honestly.
Two practical caveats. The letters are drawn with a bold monospace typeface scaled so the capital height matches the calculated figure; true Snellen optotypes are drawn on a 5×5 grid, so stroke widths are an approximation even though the overall height is exact. And clinics standardise on 6 m / 20 ft because at that range the eye's focusing effort is essentially relaxed - shorter distances stay geometrically valid but ask more of your focusing muscles, which is worth knowing if you test at 1 m on a phone.
One accuracy bound worth stating: letters are drawn on a pixel grid, so each row is rounded to the nearest whole pixel. Measured on a 96 PPI display, every row lands within one pixel of its calculated height - about 3% on the 20/20 row and well under 1% on the larger rows. That is comfortably inside a single row's step, since consecutive rows differ by 20-25%.
FAQ
Is this a substitute for a real eye exam?
No. This is an informal screening aid, not a medical device and not a diagnosis. Even with the screen calibrated, lighting, screen quality, and how accurately you measure your distance all affect the result. See an optometrist or ophthalmologist for a real examination, and seek urgent care for any sudden change in vision.
How do I check my eyesight on a phone?
Calibrate the chart with a bank or ID card held against the screen, then choose a distance you can actually achieve indoors - 1 m or 1.5 m works on a phone. A phone screen is too narrow to show the 20/200 row at 6 m, and the tool tells you when the chart no longer fits so you can move closer instead of reading a chart that is silently cut off.
Why do I have to calibrate the screen with a card?
A browser cannot find out the physical size of your display - it only knows CSS pixels, which are a different physical size on every device. Matching the outline to a bank or ID card, which is 85.60 mm wide under ISO/IEC 7810 ID-1, tells the chart how many pixels make a millimetre. Without that step, an on-screen chart cannot honestly label any row as 20/20.
Why does viewing distance matter?
An optotype only has a correct size once you fix a distance. This chart recalculates every row from the distance you choose, so the letters are drawn to subtend the right angle at your eye. If you then stand somewhere else, the labels no longer apply - move to the distance you selected, or change the selection to match where you are.
What does "20/20" mean?
20/20 means you can read at 20 feet what a person with standard vision reads at 20 feet. 20/100 means you have to be at 20 feet to read what they read at 100 feet. The same thing is written 6/6 and 6/30 in metres. It describes sharpness only - not colour vision, depth, or eye health.
How is each row sized?
A Snellen optotype is defined to subtend five arcminutes at its reference distance, with the strokes and gaps subtending one arcminute. The chart uses w = 2 x d x tan(theta / 2) with theta = 5 arcminutes scaled by the row, the standard formula. As a check: at exactly 6 m this produces 8.73 mm for the 6/6 row and 87.3 mm for the top 6/60 letter, which are the published figures for a physical chart.
Can I use the fullscreen view for a more accurate test?
Fullscreen removes browser chrome and gives the chart the whole display, which helps at longer distances where the largest rows need real estate. It does not change the letter sizes - those come from your calibration and distance, and stay physically correct either way.
How we compare
| Feature | Online Tool Store | Toolkit Gen | Teamz Lab | Clinic chart pages |
|---|---|---|---|---|
| Screen calibrated against a standard ID-1 bank card | ✓ | ✓ | ✓ | ✗ |
| Choose your own viewing distance, in metres or feet | ✓ | ✓ | Fixed 1 m | Fixed 4 ft |
| Every row resized from that distance as you change it | ✓ | ✓ | Fixed distance only | ✗ |
| States the Snellen geometry it draws from | ✓ | ✓ | Not stated | ✗ |
| Test each eye separately, in the tool | ✓ | ✓ | ✓ | Instructions only |
Calibrating to a bank card is now the baseline for an honest on-screen chart, and the better tools all do it. Where this one differs is that the distance is yours to choose and every row is recomputed from it, so the chart works at 1 m on a phone or 6 m across a room rather than only at one distance the page picked for you - and it says so when the largest rows no longer fit your screen instead of quietly cutting them off.