What Is Reaction Time? A Plain-English Definition
By Lokesh Rathore · Updated July 4, 2026
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The first number I ever got on a reaction test was 248 milliseconds, and my honest reaction was: is that a good definition of “fast”, or is a quarter of a second just how slow we all are? It turns out the word “reaction time” gets used loosely for a few different things, so before you judge your own number, it helps to know exactly what it measures.
Reaction time is the gap between a stimulus appearing and the start of your response to it, measured in milliseconds. On a screen it is the time from the moment a color changes to the moment your finger clicks. It is not how fast you can click repeatedly, and it is not your reflexes in the medical sense; it is that single “signal, then move” delay.
A simple definition
Break the phrase into its two halves and it explains itself. There is a stimulus, the thing you react to: a light, a sound, a touch, a starting gun. Then there is your response, the action you make because of it: a click, a tap, a foot off the blocks. Reaction time is the clock running between those two events, and nothing else.
That “nothing else” matters. If you press before the signal, that is not a fast reaction, it is a guess, which is why good tests throw out anything under about 100 milliseconds. A genuine human reaction to something you did not see coming cannot beat that floor, because the signal physically has to travel from your senses to your brain and back out to your muscles first.
What happens in that gap
The quarter-second feels instant, but a whole chain runs inside it. Light hits your retina and gets converted into a nerve signal, that signal travels to your visual cortex, your brain decides what to do, and only then does the command reach your hand. The surprising part is that the sensing and the moving are the quick bits. Most of the time goes on the decision in the middle. If you want the full step-by-step, I wrote a separate piece on the science of reaction time.
The main types of reaction time
“Reaction time” is really an umbrella for a few different measures, and mixing them up is where most confusion comes from.
- Simple reaction time. One signal, one response. Green means click. This is the classic test and the fastest of the three.
- Choice reaction time. Several possible signals, each with its own response. This is slower, because now you have to decide, not just react. The slowdown follows a rule called Hick’s law, covered in simple vs choice reaction time.
- Recognition (go / no-go) reaction time. Respond to some signals and hold back on others. It measures whether you can stop yourself as well as go, which you can try on the go / no-go test.
There is also a split by sense. A visual reaction to light is the most common online, but an auditory reaction to sound is usually a touch quicker, and a tactile reaction to touch is quick too. The ordering and the reasons are in auditory vs visual reaction time.
Everyday examples of reaction time
It is easier to picture with real ones:
- A driver seeing brake lights ahead and moving their foot to the pedal.
- A goalkeeper starting to dive as the ball leaves the striker’s boot.
- A sprinter pushing off the blocks when the gun fires.
- A gamer flicking their aim onto an enemy that just appeared.
- Catching a glass you knocked off the table before it lands.
In every case it is the same thing: a signal, then the very start of a response. The driving one even has real consequences, since the metres your car travels during that gap become part of your stopping distance, which is the whole point of the driving reaction time test.
How reaction time is measured
The unit is the millisecond, one thousandth of a second, because human reactions live in the hundreds of them. A typical online result is around 273 milliseconds, drawn from very large public datasets of click tests. In a lab, where there is no browser adding delay, a simple visual reaction is quicker, roughly 200 to 250 milliseconds.
That difference is not your biology changing, it is the equipment. Any browser test adds 10 to 50 milliseconds of screen and input lag on top of your true reaction, so the same person reads slower online than on lab hardware. A good test measures that lag and tells you about it rather than hiding it, which is what our reaction time test does, and the exact method is on the methodology page.
Why it is worth knowing your own number
Once you know what reaction time actually is, your own result stops being a mystery number and becomes something you can read: where you sit against everyone else, how it shifts with age, and how much of a “slow” score is really just tiredness or a trackpad. If you have a number already, you can check whether it is any good on the is my reaction time good? page, or just take the test and find out.
Sources
- Human Benchmark, Reaction Time statistics (public dataset, 81M+ clicks; median around 273 ms)
- Talboom et al. (2021), npj Aging, MindCrowd online reaction-time study
- Proctor and Schneider (2018), Hick’s law review, Quarterly Journal of Experimental Psychology
Written by Lokesh Rathore, Founder of ReactScore. Lokesh Rathore is the founder of ReactScore and the person behind everything on it. Reflexes and reaction time are a genuine fascination of his, so he built the test he wanted to use himself: one that measures honestly, corrects for the lag your screen and mouse add, and explains the numbers instead of hiding them. He keeps every figure on the site grounded in public datasets and published research. More about the author · how we measure →