How to use the reaction time tester
- Press Start test and wait while the panel is red.
- Click, tap or press Space the moment it turns green.
- Repeat for five tries. The tester shows each time and then your average.
If you respond before green, the try is discarded and repeated. The wait before green is random, between about 1.5 and 5 seconds, so the result reflects reaction and not rhythm.
How the timing works
The tester uses the browser’s high-resolution clock, which reports time in fractions of a millisecond. It starts timing at the animation frame in which the green panel is drawn and stops when your input event arrives.
What it cannot see is the delay outside the browser:
| Source of delay | Typical size |
|---|---|
| Waiting for the next screen refresh at 60 Hz | Up to 16.7 ms |
| Panel response and display processing | 5 to 30 ms, more on some TVs |
| Mouse, keyboard or touch input | 1 to 20 ms |
These add up, which is why online testers report averages around 270 ms while lab equipment records 200 to 250 ms for similar people.
Getting an accurate reading
Keep the hardware constant. Use the same device, browser and input method each time you test.
Close what you can. Heavy background tabs and programs can delay frames.
Use the average, not the best. One fast click is often partly luck. The five-try average, and the running average in the Your scores panel, are far steadier.
Take several runs. Three runs of five tries give fifteen measurements, enough to see your real level.
Using it as a hardware check
Because your own reaction time is fairly stable, the tester doubles as a rough latency comparison. Switch from a TV to a monitor, from wireless to wired, or from 60 Hz to 144 Hz, and the change in your average shows roughly how much delay you removed.
For score bands and the science behind the numbers, see the reaction time test guide or read about human reaction time.