IQ, short for intelligence quotient, is one of the best-known ideas in psychology and one of the most misunderstood. People treat it as a fixed measure of how "smart" someone is, but an IQ score is more specific and more limited than that. This guide explains what IQ tests measure, how scores are calculated, and what to keep in mind if you take one.
What is an IQ test?
An IQ test is a standardised set of tasks that measure cognitive abilities such as reasoning, problem-solving, working memory, processing speed and verbal or spatial skills. Your performance is compared with a large reference group of people of the same age, and the result is turned into a score.
A short history
The first practical intelligence test was developed by Alfred Binet and colleagues in France in the early 1900s to identify children who needed extra help at school. The term "intelligence quotient" originally described mental age divided by chronological age. Modern tests, such as those in the Wechsler family, no longer use that formula. Instead they compare you with others of your age using a statistical distribution.
How is an IQ score calculated?
Modern IQ scores are usually set so that the average score in the reference population is 100. On Wechsler-style scales, the standard deviation is 15, which describes how spread out scores are. On this scale:
- About two-thirds of people score between 85 and 115.
- About 95% score between 70 and 130.
- Scores above 130 or below 70 are each found in only a small percentage of people.
A score is therefore a statement of where your performance falls compared with your reference group, not a measure of your worth or potential.
What do IQ tests measure?
Most professional tests assess several abilities and combine them. Common areas include:
- Fluid reasoning: solving new problems, spotting patterns, thinking logically without relying on prior knowledge. Matrix puzzles measure this.
- Verbal comprehension: vocabulary and understanding of language and concepts.
- Working memory: holding and manipulating information in your mind.
- Processing speed: how quickly you can carry out simple tasks accurately.
- Visual-spatial skills: understanding shapes and spatial relationships.
Culture-fair tests
Because language and schooling can influence test performance, some tests use non-verbal, pattern-based questions, such as completing a matrix of shapes. These are often described as "culture-fair" because they rely less on language and school knowledge. No test is completely free of cultural influence, but these designs try to reduce it.
What IQ can and cannot predict
IQ scores are among the more reliable measures in psychology, and they are associated with academic performance, learning speed and some job outcomes. But the relationship is far from perfect. IQ does not measure:
- Creativity, curiosity or wisdom.
- Emotional intelligence, empathy or social skills. See our article on emotional intelligence.
- Motivation, persistence or conscientiousness, which strongly influence success.
- Practical skills, talent in music, sport or art, or moral character.
Two people with the same IQ can have very different strengths and life outcomes.
Is IQ fixed?
IQ is fairly stable in adulthood, but not fixed. Scores in childhood can change with schooling, health, nutrition and environment. Population IQ scores also rose through much of the twentieth century, a pattern known as the Flynn effect, which suggests environmental influences matter. Practice on similar puzzles can raise your score on that test, but this does not necessarily mean that your underlying ability has changed.
Are online IQ tests accurate?
It varies a lot. Professional IQ tests are individually administered by a trained psychologist and cannot be replicated online. Online tests can offer a rough indication of reasoning ability if they are properly built, standardised and honest about their limitations. Signs of a better online test include a clear description of what it measures, standardised scoring, age-appropriate versions and no promises of a "genius" score for everyone. Be cautious about tests that ask for payment before showing a vague result. Our article on how accurate online tests are gives more guidance.
PsiQ's online IQ test offers age-stratified versions for ages 4 to 75+, with culture-fair pattern-based items and Wechsler-style scoring with an SD of 15.
Tips if you take an IQ test
- Take it when you are rested and undistracted.
- Read the instructions carefully, and follow any time limits.
- Do not worry about a single result. Performance varies from day to day.
- Treat the score as one piece of information about your cognitive strengths, not as a label.
IQ and other aspects of who you are
Abilities are only one part of the picture. Personality traits such as conscientiousness and openness also shape how people use their abilities. You can explore this side with our personality tests and our guide to the Big Five personality traits.