Online Tool Store
Eye Test Chart
Calibrate your screen with a bank card, pick a viewing distance, then read an interactive Snellen chart one line at a time. A screening self-check, not a medical diagnosis. Results per eye.
This works right here on your device — nothing gets sent out.
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Prepare
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Calibrate
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Choose eye
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Test
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Result
Get ready for your vision screening
You’ll calibrate your screen, pick an eye, then read letters that get smaller one line at a time — just like a printed eye chart.
- Wear your normal distance glasses or contacts if you use them.
- Sit at the recommended viewing distance for the whole test.
- Use comfortable, normal screen brightness — not maximum.
- Test one eye at a time, covering the other without pressing on it.
- Keep your head straight and look directly at the screen.
Calibrate your screen
Match the on-screen width to a standard bank or ID card so every letter is drawn at its true physical size.
Choose a distance you can keep for the whole test. Every line is sized for it.
Choose which eye to test
Test each eye separately for a real screening, or both together for a quick check.
Testing: Right Eye
Read the letters above, then tap them in order below.
Screening result
This is your measured visual acuity on this screen-based test — the smallest line you read correctly under today’s conditions. It is a screening result, not a diagnosis.
This is an online screening tool, not a medical device and not a diagnosis. Results depend on your screen size, resolution, brightness, calibration, and viewing distance. It is not a substitute for an eye examination — see an optometrist or ophthalmologist for a real one, and seek urgent care for any sudden change in vision. Nothing you enter here is uploaded; it only exists in this browser tab.
How the eye test chart works
- Prepare: run through a short checklist covering glasses, distance, brightness, and testing one eye at a time.
- Calibrate once: hold a bank or ID card against the screen and drag the slider until the outline matches it, then pick the viewing distance you can actually manage. Every line is drawn from that distance.
- Choose right eye, left eye, or both. For a single eye, the tool reminds you which one to cover.
- Read the interactive test: one randomized line at a time, largest first. Tap the letters you see on the keypad and submit - the answer is never shown first. Use fullscreen if a line feels crowded.
- The test stops once a line is no longer read correctly. Your result is the smallest line you got at least half right, shown in 20/x, 6/x, decimal, and logMAR notation, with the option to test the other eye or retest.
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 the formula below, where d is your viewing distance and θ is five arcminutes scaled by the row's denominator.
w = 2 × d × tan(θ / 2)
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, though 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, so shorter distances stay geometrically valid but ask more of your focusing muscles, 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, 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 a line no longer fits so you can move closer instead of reading a chart that is silently cut off.
How does the interactive test work?
After you calibrate and pick an eye, the tool shows one randomized line at a time, largest first, and asks you to tap the letters you see on an on-screen keypad. It never reveals the correct letters before you submit. A line counts as read once you get at least half its letters right; the smallest line you read that way becomes your result for that eye.
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 |
| Interactive line-by-line test with a letter keypad | ✓ | Static chart only | Static chart 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 line 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 walks you through an actual guided screening, one randomized line at a time with a submit step, instead of a static chart you self-grade by eye.