Reaction Time Test
Measure your reaction time in milliseconds. Wait for the green screen, then click as fast as you can.
How to play
- Click the red box to start — it will say "Wait for green…".
- Wait patiently. The box turns green at a random delay (1.5–4.5 s).
- Click the green box as fast as possible when it appears.
- Your reaction time in milliseconds is shown. Click again to retry.
- Avoid clicking early — the test detects false starts and resets.
Wait for the box to turn green, then click as fast as possible. Measures your visual reaction time in milliseconds. Average human reaction time is around 200–250 ms.
How it works
The Reaction Time Test measures how quickly you can respond to a visual stimulus. The screen starts red, and after a random delay the background turns green. The moment you see green, click as fast as you can. Your response time is displayed in milliseconds from the color change to your click.
The random delay before the green screen prevents you from anticipating the signal. This isolates simple reaction time -- the time your nervous system takes to detect a stimulus and send a motor command to your hand -- rather than decision-making speed.
Average human simple reaction time to a visual stimulus is roughly 200 to 250 milliseconds. Factors such as fatigue, caffeine, display lag, and mouse hardware all influence your score. Run several trials and look at your average rather than any single result.
This test is used informally to track daily cognitive readiness, compare alertness before and after sleep or exercise, or simply compete with friends for the fastest time.
Worked example
Getting a reliable baseline score
- Sit with your hand resting on the mouse and your eyes focused on the center of the screen.
- Click Start and wait without anticipating -- do not watch the edges of the screen for clues.
- The moment the screen turns green, click immediately.
- Note your result, then repeat the test five more times.
- Discard outliers and average the rest to get a stable baseline.
A stable baseline reaction time in milliseconds.
Common mistakes to avoid
- Clicking rapidly in anticipation before the green screen appears, producing false starts that inflate the average.
- Testing on a touch screen or trackpad, which adds input latency and raises scores compared to a mouse.
- Running only one trial and treating it as representative when a single result can vary by 50 ms or more due to normal variability.
Key terms
- Simple reaction time
- The delay between a single expected stimulus appearing and your motor response, measured in milliseconds.
- False start
- Clicking before the screen turns green; results in a penalty or invalid trial because you anticipated the signal.
- Display lag
- The delay between a signal being sent and the pixel actually changing color on your monitor; this adds a small constant to all scores.
Frequently asked questions
- What is a good reaction time?
- The average human reaction time is 200–250 ms. Elite gamers and athletes often hit 150–180 ms. Under 200 ms is excellent.
- Why does clicking too early reset it?
- Anticipating the signal (false start) doesn't count as a true reaction — the test waits for you to actually respond to the visual cue.