Reaction tests

A reaction test measures the time between a signal and your answer to it: a screen that turns green, a light that goes out, a sound. The signal is the same every time and the answer is a single press, so the number you get is about you and not about the task. It is your reaction time, which is not the same thing as how fast you think.

Because the answer is so simple, a reaction test is quick to take and easy to repeat. That is what makes it useful: you can try again tomorrow, or on another device, and see what changes.

Nobody reacts at exactly the same speed twice. Tiredness, the time of day, how much you expected the signal and the device in your hand all change the result a little. That is why a test uses several tries and shows the middle one, and why one fast try tells you less than a few in a row.

If a try is too early, the test does it again. If you look away, that try does not count. Neither is held against you.

Use a device you know well, sit comfortably and keep the screen in front of you. A phone, a laptop and a mouse all work, and each one adds its own small delay, which a browser cannot measure. For a fair look at how you are changing, use the same device each time.

Children and older visitors are welcome to take every test at their own pace. Nothing here runs on by itself: you decide when each try begins, and you can stop whenever you like.

In a careful laboratory study of 1,469 adults aged 18 to 65, the average simple reaction time to a light was 230.8 ms^[1]. Trained sprinters can start their muscles in under 85 ms after a gun^[2], and reaction time slows only a little with age. Our Facts articles explain what a really good reaction time is and how it changes with age.