What is a good reaction time?

The kind our challenge measures is called simple reaction time: one signal, one response, and nothing to decide. You know what is coming and what to do. You just don't know when.

There is also choice reaction time, where you have to pick the right response to one of several signals, such as pressing a different key for each color. Choosing takes extra time, so choice reaction times run longer than simple ones.

Reaction times are measured in milliseconds (ms), thousandths of a second. A quarter of a second is 250 ms.

In one of the larger computer-based studies, David Woods and colleagues measured simple reaction time in 1,469 adults aged 18 to 65 in New Zealand. The average was 231 ms. In a second group of 189 people aged 18 to 82 in California, it was 238 ms.

The team also measured their own equipment. Their screen added 11.0 ms and their mouse 6.8 ms, nearly 18 ms in all. Taking that out brought the averages down to about 213 and 220 ms.

Other computer-based studies have reported averages from about 233 ms to nearly 400 ms. The authors point out that hardware delays alone can add up to 100 ms to a measured time, and that the screen, the button and the way a test is run all play a part. A good share of the spread between studies may come from the equipment rather than the people.

Woods and colleagues also cite visual reaction times of about 181 to 189 ms recorded by Francis Galton in Victorian England, quicker than most modern computer studies. Comparing numbers measured in very different ways is risky.

Because the equipment matters so much, it helps to think in rough ranges rather than chasing one target. Our challenge sorts results into five bands, from Hair Trigger (under 180 ms) to Scenic Route (380 ms or more). The middle band, Right On Time, runs from 230 to 289 ms, which is where the averages in Woods' study fall when they include the delay from ordinary computer equipment.

• Under about 200 ms on a phone or laptop is quick. It's worth another try to check it wasn't a well-timed guess.
• Anywhere in the 200s is ordinary for a browser test.
• Over 300 ms often means something got in the way: a slow screen, a moment of distraction, or a finger that wasn't ready.

We don't rank you against other players or tell you what percentage of people you beat. We haven't collected the kind of data that would make a claim like that honest.

Every reaction time from a test like ours includes the device. The screen has to draw the green, and your tap or click has to travel through the touchscreen or mouse, the operating system and the browser before it is counted.

A screen that refreshes 60 times a second shows a new picture every 16.7 ms, so even drawing the green takes a moment. Touchscreens, wireless mice and keyboards each add a delay of their own, and that delay differs from one device to the next.

Our challenge starts the clock at the moment the green is actually drawn on your screen, not when our code asks for it, which removes one source of error. The rest, from the touchscreen to the browser, is built into your number. That is why comparing your own scores on one device tells you more than comparing a phone score with a laptop score.

Even on the same device, your time moves around. Research points to a few reasons.

• Age. In Woods' study, simple reaction times rose by about half a millisecond a year, roughly 5 ms a decade. In a survey of more than 7,000 adults in the UK, Geoff Der and Ian Deary found that simple reaction time changes little until around age 50, while choice reaction time slows throughout adult life.
• Lost sleep. In a review of 70 published articles, Julian Lim and David Dinges found that going without sleep for up to two days had its largest effect on lapses in simple attention: moments when attention drops out and a response comes far too late.
• Tiredness during a session. In Woods' study, average times crept up from 228 ms in the first block of 20 trials to 237 ms in the last, which the authors put down to fatigue.
• Expectation. A simple reaction test rewards staying ready, and anyone who can predict the moment can start moving early. That's why our challenge waits a random time, between 1.5 and 4.5 seconds, before each green.
• Men and women. Woods and colleagues found no significant difference between men and women in simple reaction time. Der and Deary did find differences between the sexes, most clearly in how much choice reaction times varied.

None of these is a reason to worry about a single score. They are reasons not to read too much into one.

Over five rounds, one round is often an outlier: a lucky early tap, or a moment when your attention drifted. An average lets that one round pull your score up or down. The middle value, called the median, ignores both ends.

Say your five rounds were 231, 245, 238, 410 and 252 ms. The average is 275 ms, dragged up by the 410. The median is 245 ms, much closer to how you did on a typical round. That is the number our challenge shows.

Sprinting draws a similar line. In elite races, World Athletics-certified start systems record how quickly each runner responds to the gun, so that nobody gains an unfair advantage by responding less than 100 ms after it. A sprinter reacts to a sound and our challenge asks you to react to a color, but the idea is the same: below a certain time, a response is more likely to be anticipation than reaction.

The exact line is debated. A 2021 review by Milloz, Hayes and Harrison notes that the 100 ms threshold has been criticized for lacking scientific evidence, and calls for research to pin down the fastest genuine reaction. A browser adds delays of its own on top, so our challenge plays it safe and treats any time under 100 ms as a guess.

• Use the same device each time if you want to compare your scores.
• Play when you can watch the pad without being interrupted.
• Keep your finger just above the screen, or rest it on the space bar on a computer.
• Don't try to guess the green. A tap before it turns green doesn't count, and a time under 100 ms is treated as a guess and thrown out.
• Try a few runs. Your best on each device is kept in that browser, so you can see how much your score moves from one run to the next.

This challenge is for fun. A reaction time from a browser isn't a medical, cognitive or fitness assessment, and it says nothing about your health or intelligence.