How the reaction time test works
Press Start. The screen keeps its color while a random delay runs, somewhere between 1.5 and 5 seconds. Then the whole screen turns white at once. Tap anywhere, click, or press the space bar as fast as you can. The time between the white screen and your tap is your reaction time, shown in milliseconds (ms): 1,000 ms make one second.
You get five tries. Between two tries, tap once more to start the next wait. At the end, the big number is your average, the white box marks your best try, and your record is kept on this device for next time. If you tap before the screen turns white, it is a false start: that try does not count and you simply go again.
A time under 100 ms is also refused. Nobody can see a change and move a finger that fast, so such a tap is a lucky guess. Sprinting uses the same limit: in World Athletics races, an athlete who leaves the blocks less than 0.100 seconds after the gun is charged with a false start.
What is a good reaction time?
For a simple visual signal, lab studies with dedicated equipment usually find averages around 180 to 250 ms. A literature review by Robert Kosinski (Clemson University), quoted by the BioNumbers database of Harvard Medical School, gives about 180 to 200 ms for light and 140 to 160 ms for sound. A 2012 study of 90 people in India (Deore and colleagues, Journal of Clinical and Diagnostic Research) measured visual averages between 209 and 232 ms depending on the group.
Online tests are a little slower, because your screen, your mouse or your touchscreen add their own delay. That is why about 250 ms is a typical online result, and the number this test shows before your first try.
| Your average | What it means online |
|---|---|
| Under 200 ms | Excellent, well under the typical online result. |
| 200 to 250 ms | Fast, better than the typical online result. |
| 250 to 300 ms | Typical. Most people land here. |
| Over 300 ms | On the slow side. Try again rested, with a mouse or the space bar. |
Do not compare a phone score with a computer score: the equipment is part of the measure. Compare yourself with yourself, on the same device.
Why your device changes the result
A screen refreshes a fixed number of times per second. At 60 Hz, a new image appears every 16.7 ms, so the white screen can only show up at the next refresh. Then the panel needs a few milliseconds to switch its pixels, and your tap has to travel back: touchscreens scan for fingers at their own rate, wireless mice and Bluetooth keyboards add a short radio delay. All of this ends up in your score.
This test does what it can to stay fair. It starts the clock on the first frame in which the white screen is actually drawn, not when the code asks for it, and it reads the exact time stamp of your tap or key press, not the moment the page gets around to handling it. For your best result, use a computer with a wired mouse or the space bar, and close heavy tabs.
Light or sound: which is faster?
We react faster to sounds than to lights: about 140 to 160 ms for a sound versus 180 to 200 ms for a light, in the figures quoted above. That is one reason why races start with a gun rather than a light. A study commissioned by the IAAF (now World Athletics) on national-level Finnish sprinters even recorded simple sound reactions as fast as 80 ms, and its authors suggested lowering the 100 ms limit to 80 or 85 ms. The rule did not change: in 2022, hurdler Devon Allen was disqualified at the World Championships for a reaction of 0.099 seconds, one millisecond under the limit.
What slows you down, and what helps
Reaction time is not fixed. Tiredness, lack of sleep, alcohol, distraction and some medicines make it slower. Age plays a part too: reactions tend to slow as we get older. Warming up, focusing on the screen and practice help a bit. The delay changes at random on every try, so you cannot learn the rhythm and anticipate. That is the point: the test measures how fast you react, not how well you guess.
Tips for a better score
- Sit comfortably, finger already resting on the space bar or the mouse button.
- Look at the center of the screen, not at your hand.
- Do not try to guess the moment. React to the white, nothing else.
- Do two or three rounds: the first one is often a warm-up.
- Rest your eyes between rounds. A short breathing exercise helps you settle.
Want to test your timing differently? Try to stop the stopwatch exactly on 10.00 seconds, or play along with the metronome and see if you stay on the beat. For kids, the learn to tell time games are another way to play against the clock.