How this Stroop test works
Press Start test and 24 colour words appear one after another: RED, GREEN, BLUE and YELLOW. Each word is printed in one of the same four ink colours. Your job is to answer the ink colour, not the word, by tapping Red, Green, Blue or Yellow, or by pressing the keys 1 to 4 on a keyboard.
Half of the rounds are matching (the word BLUE printed in blue) and half are mismatched (the word BLUE printed in red). The order is shuffled, and the same ink colour never appears twice in a row when it can be avoided. A short cross appears between words so you know where to look. A wrong answer flashes a red border and the test moves on. Holding back the wrong answer is also the core skill in the choice reaction time test, where a red hand tells you not to press.
The timer for each word starts when the word is drawn on screen and stops when you answer. Everything is measured in your browser.
How to read your result
Your score is the Stroop effect:
Stroop effect = your average time on mismatched words − your average time on matching words
Only correct answers are used for the averages. The result card also shows both averages and how many of the 24 words you got right.
- A smaller number is better. It means the written word got in your way less. A result near zero, or even slightly negative, is possible on a single run, because 12 words per condition is a small sample.
- Under 50 ms, the word barely slowed you down this round. 50–119 ms is mild interference, 120–199 ms is clear interference and 200 ms or more is strong interference. These bands are only labels for this test, not norms from a study.
- Accuracy matters. If you got fewer than 80% right, the card warns you, because rushing changes the timing. If you have no correct answer in one of the two conditions, no Stroop effect can be calculated and nothing is saved.
We do not show a "typical" value. Published Stroop studies use different set-ups (reading lists aloud, voice keys, different numbers of colours), so their numbers are not comparable with a four-button version on a phone or laptop. The fair comparison is with yourself: your personal best and your last results are kept in this browser.
Why the word gets in the way
For a fluent reader, reading is automatic. You cannot look at a familiar word and not read it. Naming a colour, on the other hand, takes a deliberate step. When the word and the ink disagree, the automatic answer (the word) has to be held back while the slower answer (the colour) is selected. That extra control takes time, and it sometimes fails, which is why most mistakes happen on mismatched words.
The effect is named after John Ridley Stroop, who described it in 1935. In his experiments, naming the ink colours of conflicting colour words took clearly longer than naming the colours of plain squares, while reading the words was hardly affected by the ink. Colin MacLeod's 1991 review of more than 50 years of research showed how robust the effect is: it appears in almost every fluent reader, and it has become one of the standard tasks for studying attention and self-control. To see how well you keep that control over several minutes, try the attention span test.
What affects your score
- Practice. Your second and third runs are usually faster and often show a smaller effect, because you get used to the buttons. Compare results after a couple of warm-up rounds.
- Tiredness and stress. Holding back an automatic answer is effortful, so the effect tends to be larger when you are tired or distracted.
- Language. The test uses colour words in the page language. If you are not fluent in that language, the word is read less automatically and the effect may be smaller. That says nothing about your attention.
- Your device. Display delay and touch delay add the same amount to both conditions, so they mostly cancel out in the difference. That is one advantage of scoring the effect rather than raw speed.
Colour vision and other limits
This test depends on telling red, green, blue and yellow apart. If you have red–green colour blindness, the result will not be fair, and a color blind test is a better place to start. Strong screen filters such as night mode or a blue-light filter can also make the colours harder to tell apart, so turn them off for a cleaner result.
An online Stroop test is a game-like self-check. Clinical and research versions use controlled conditions and validated norms. Your result is not a measure of intelligence and is not a medical or psychological diagnosis. If you have real concerns about your attention or concentration, talk to a qualified professional.
More tests of attention, memory and thinking are on the memory and brain tests page.
Sources
- Stroop, J. R. (1935). Studies of interference in serial verbal reactions. Journal of Experimental Psychology, 18(6), 643–662.
- MacLeod, C. M. (1991). Half a century of research on the Stroop effect: An integrative review. Psychological Bulletin, 109(2), 163–203.
Frequently asked questions
What is the Stroop effect?
It is the slowdown you experience when you have to name the ink colour of a word that spells a different colour, such as the word RED printed in blue. Reading the word is automatic, so it competes with the colour you are trying to name.
How is my score calculated?
Your score is your average response time on mismatched words minus your average response time on matching words, in milliseconds. Only correct answers are used. A smaller number means less interference.
Can my Stroop effect be negative?
Yes, on a single run. Each condition has only 12 words, so chance variation can make the matching words slightly slower. Play a few rounds and look at your personal best and your recent results.
Is there a normal or average Stroop score?
Not one that fits this version. Published studies use different set-ups, such as reading lists aloud or using a voice key, so their numbers are not comparable with a four-button test on a phone or computer. Compare your own results over time instead.
Does this test work if I am colour blind?
Not fairly. The test relies on telling red, green, blue and yellow apart. With red–green colour blindness the result reflects colour discrimination, not interference.
Why do I get faster with practice?
You learn where the buttons are and get used to the task, so your average times drop. The effect itself often shrinks a little too. That is why results after a few warm-up rounds are more comparable.
Does the Stroop test measure intelligence or ADHD?
No. It measures how much a written word interferes with naming a colour in this one task. It is a self-check for curiosity and practice, not an intelligence test and not a diagnosis.