Online Snellen Eye Chart

The Snellen chart is the standard tool eye care professionals use to measure visual acuity, which is how clearly you can distinguish letters or shapes at a given distance. I built this online version because I wanted a quick way to check whether my vision had changed between annual appointments. It runs right in your browser and uses your screen to display the familiar rows of letters, starting with a large E at the top and getting progressively smaller toward the bottom.

To get a meaningful result, you need to stand at the correct distance from your screen and cover one eye at a time. The smallest row you can read accurately corresponds to a Snellen fraction like 20/20 or 20/40. That fraction tells you what you can see at 20 feet compared to someone with standard vision. Before anything else, the tool walks you through a short calibration step so the letter sizes on your specific monitor are physically accurate. Without that calibration, screen pixel density varies too much between devices for the sizes to mean anything.

Keep in mind that this is a rough screening, not a medical exam. Factors like screen glare, room lighting, and the font rendering on your device all affect accuracy. It cannot detect astigmatism, peripheral vision problems, or eye diseases. If you notice a change in your results or if reading the smaller lines is harder than it used to be, schedule a visit with an optometrist for proper testing with controlled equipment.