What is IQ? Meaning, scale and what it can’t tell you
IQ stands for intelligence quotient: a score from a standardised test that estimates reasoning ability compared with other people of the same age. Here is where the idea came from, how the scale works and what a score can and cannot tell you.
What does IQ mean?
IQ stands for intelligence quotient. Today it is not literally a quotient. Modern tests convert your performance into a standard score by comparing it with a large reference group, called the norm group, made up of people your age. The scale is set so that the average is 100 and the standard deviation is 15, which means about two thirds of people score between 85 and 115. The IQ score chart shows every range.
A short history of IQ tests
- 1905: Alfred Binet and Théodore Simon in France created the first practical intelligence scale, to identify schoolchildren who needed extra support.
- 1912: William Stern proposed the “intelligence quotient”: mental age divided by chronological age, multiplied by 100.
- 1916: Lewis Terman at Stanford revised Binet’s scale into the Stanford–Binet test, which popularised IQ in the United States.
- 1939: David Wechsler published the Wechsler–Bellevue scale. Its successors, the WAIS for adults and the WISC for children, use the modern “deviation IQ” based on norm groups.
What do IQ tests measure?
A full IQ test combines several abilities: verbal comprehension (vocabulary and word reasoning), visual and spatial reasoning, fluid reasoning (solving new problems), working memory and processing speed. Short online tests usually sample just one or two of these. Our free IQ test samples four reasoning skills, explained on how our IQ test works.
Fluid and crystallised intelligence
Psychologists Raymond Cattell and John Horn distinguished two broad kinds of ability. Fluid intelligence is the ability to solve unfamiliar problems, such as spotting the rule in a pattern. Crystallised intelligence is accumulated knowledge and skill, such as vocabulary. Fluid ability tends to peak in early adulthood, while crystallised knowledge tends to keep growing well into later life.
What does IQ predict, and what does it not?
IQ scores are associated with school achievement and, more modestly, with job performance. But they leave most of the variation in life outcomes unexplained. Motivation, effort, health, opportunity, relationships and plain luck all matter. An IQ score says nothing about someone’s worth, character or creativity.
Can your IQ change?
IQ scores are fairly stable in adulthood, but not fixed. Education, health, sleep and stress can all affect performance. Practising a particular test format mostly improves your score on that format, which is why we suggest waiting at least four weeks before retaking a test. Across the 20th century, average raw scores on IQ tests rose in many countries by roughly three points per decade, a pattern known as the Flynn effect, which is why tests are periodically re-standardised.
Common misconceptions
- “IQ is a single, exact number.” Every score has a margin of error, which is why good reports give a range.
- “A high IQ guarantees success.” It helps with some tasks, but it is one factor among many.
- “An online test can confirm giftedness.” Only a supervised assessment by a qualified professional can. See online vs professional IQ tests.
IQ FAQ
What does IQ stand for?
IQ stands for intelligence quotient. It is a score from a standardised test that estimates reasoning ability compared with other people of the same age.
Is IQ genetic?
Both genes and environment contribute to differences in IQ scores. Education, nutrition, health and the learning environment all matter, which is why the question has no simple percentage answer that applies to every person.
What is the highest possible IQ?
There is no fixed maximum, but scores far above about 160 cannot be measured reliably because too few people score that high to build trustworthy norms. Claims of extremely high IQ numbers should be treated with caution.
Is IQ the same as intelligence?
No. IQ measures certain cognitive abilities such as reasoning, memory and verbal comprehension. Intelligence is a broader idea that also includes creativity, practical skills and social understanding, which IQ tests do not capture well.