How to use it
- Click or tap the box (or press Space) to start. It turns red: wait.
- After a random 1.5 to 4.5 seconds it turns green. Click, tap or press Space as fast as you can. Your time for that round appears; click again for the next.
- After five rounds you get your average, median, best and slowest time. Clicking before green counts as too soon: the round is repeated and not scored.
How it measures
The green is painted at the start of a display frame, and the page records that frame’s time; your reaction is the time of your click (or key press) minus it, both read from the same high-resolution browser clock. That measures the browser’s part exactly, but every setup adds its own delays the page cannot see: the monitor takes some milliseconds to show a new frame, and a mouse or keyboard takes some to report a press. Laptops, wireless mice and phones differ, so compare your times on the same device. The median is less swayed by one slow round than the average.
What is a normal reaction time?
In 2015 David Woods and colleagues built a calibrated, high-precision version of this kind of test and measured 1,469 adults aged 18 to 65. The mean simple visual reaction time was 231 ms, or 213 ms after taking out the measured delays of their own equipment; it rose with age by about 0.55 ms a year and did not differ by sex or education. They also note that published averages from less carefully timed computer tests range from about 233 ms to nearly 400 ms, partly because of hardware and software delays like the ones described above. So a result in the mid-200s here is ordinary; if yours is far higher, try a wired mouse or a different screen before blaming your reflexes.
What we tested
On October 15, 2026, in Chromium: a script waited for the green frame, then clicked after a fixed 120, 250 or 400 ms. In every round the page’s time equalled the delay from the green frame to the click to the millisecond; it was 4 to 17 ms longer than the script’s own delay because the script itself only noticed the green a few milliseconds after the frame began. A click during the wait showed “Too soon” and was not counted, Space started a round, the random wait stayed between 1.5 and 4.5 seconds, and the page fits a 390 px screen.
Sources
- David L. Woods, John M. Wyma, E. William Yund, Timothy J. Herron and Bruce Reed, Factors influencing the latency of simple reaction time, Frontiers in Human Neuroscience 9:131 (2015).
Frequently Asked Questions
Built by Derek Giordano · Part of Ultimate Design Tools