Reaction Time Test

How the reaction time test works

Click the box to start a try. It turns red, and after a random wait between 1.5 and 5 seconds it turns green. Click, tap or press Space as soon as you see green. The time between the green box appearing and your press is your reaction time, shown in milliseconds (ms), where 1,000 ms make one second. Five tries make one round, and after each round you get your average, your best single try and a small chart of all five.

People often call this a reflex test, but strictly speaking it measures a reaction, not a reflex. A reflex, like the knee jerk when a doctor taps below your kneecap, happens automatically. Here you have to see the change, decide it is time and then move your finger on purpose.

The random wait matters. If the green came after the same pause every time, you could learn the rhythm and press in anticipation instead of reacting. Clicking while the box is still red shows "Too soon" and that try does not count. A press less than 110 ms after the green appears is also rejected as a guess; the 2015 study described below used the same lower limit when it counted valid responses.

How the timing is measured

The test uses the browser's high-resolution clock, performance.now(), rather than the ordinary clock. MDN Web Docs gives its resolution in a normal web page as 100 microseconds, a tenth of a millisecond. The start time is taken in the same animation frame in which the green box is drawn, and the end time is the time stamp the browser gives the press event. The test reacts when the mouse button, the finger or the key goes down, not when you let go.

That makes the browser part of the measurement tight, but two delays outside the web page are always included, and no web page can remove them:

• The screen. A monitor only shows a new picture at its refresh rate, and its electronics need a moment to put it on the panel. In the study below, the monitor alone added 11.0 ms on average, measured with a light sensor on the screen.
• The input device. A mouse, trackpad, touch screen or keyboard needs time to notice the press and report it to the computer. The study's mouse added 6.8 ms, and the authors note that standard mouse drivers can add 20 ms or more.

How long one screen refresh takes, depending on the refresh rate:

So the same person can score a few milliseconds faster on a fast gaming monitor than on an older laptop, without reacting any faster. Compare scores on the same device, and treat differences of a few milliseconds as noise.

What is a typical reaction time?

A large study of simple reaction time was published by David L. Woods and colleagues in Frontiers in Human Neuroscience in 2015. They tested 1,469 community volunteers aged 18 to 65 in Rotorua, New Zealand, who clicked a mouse button as soon as a target appeared on a computer screen. Their findings:

• The average reaction time was 231 ms as measured, or 213 ms after subtracting the 17.8 ms that their screen and mouse added.
• Reaction times grew slower with age, by about 0.55 ms per year, so roughly 5 ms per decade.
• Men and women did not differ significantly, and neither did people with different levels of education.
• Reactions were about 15% slower after the shortest wait before the target, one reason good tests vary the wait.
• Over the session, reactions got slightly slower, from 228.1 ms in the first block of 20 tries to 237.2 ms in the last, which the authors put down to fatigue.

Because every test setup has its own delays, use these numbers as a rough guide rather than a pass or fail line. Your average here includes your own screen and input device.

Tips for a fair, consistent score

• Rest your finger on the button or the key, so the press is the only movement you need to make.
• Look at the box, not the numbers. Your eyes should be on the spot where the color changes.
• Do not guess. Early clicks only cost you time, and the random wait makes guessing a losing strategy.
• Use the same device when you compare scores over days or with friends, and keep other heavy apps closed so the computer is not busy.
• Take short breaks between rounds. Long sessions make reactions slower, as the study above found.

More quick tests

Reacting fast and clicking fast are different skills. To find out how many clicks per second you can manage, try the click speed test. To time your own drills, the stopwatch records lap times.

How to use the reaction time test

1. 1Click, tap or press Space on the box. It turns red.
2. 2Wait. As soon as the box turns green, press as fast as you can. Your reaction time in milliseconds appears right away.
3. 3Click again for the next try. After five tries you see your average, your best try and the chart; click once more to start a new round, or Copy result to share it.

Frequently asked questions