What Is an IQ Test? What It Measures and How It Works

Updated 25 September 2026. About 12 minutes to read.

What is an IQ test?

IQ stands for intelligence quotient. An IQ test is a set of carefully designed tasks, such as puzzles, word problems, memory tasks and timed exercises, that measure how well you reason, learn and solve problems.

Two features separate a real IQ test from a quiz. First, it is standardised: everyone takes it the same way, with the same instructions, timing and scoring rules. Second, it is norm-referenced: before the test is published, it is given to a large sample of people chosen to match the population, and your result is compared with people of your own age in that sample.

That comparison is what turns your answers into an IQ. A score of 100 means you performed exactly at the average for your age, and every 15 points marks one standard deviation above or below. Our guide to how IQ is calculated walks through the formula step by step.

What does an IQ test measure?

Modern IQ tests do not measure one single thing. The WAIS-5, published by Pearson in 2024 for ages 16 to 90, uses 10 primary subtests to measure five broad abilities, which it calls cognitive domains.

The Full Scale IQ combines these abilities into one overall score. Psychologists see it as a summary of general reasoning ability, which researchers often call g, the common factor that links performance across very different mental tasks.

What an IQ test tells you

A professional IQ report tells you much more than one number. For each ability, it gives a score, a percentile and a confidence range showing where your true score most likely falls. That profile often matters more than the headline figure.

This person's overall IQ of 94 sits in the Average range. Their scores underneath it range from 79 to 114, a gap of more than two standard deviations. Their verbal skills are well above average, while their visual-spatial skills are well below it. A single number would hide both, which is why psychologists look closely at the whole profile when advising on learning support or workplace adjustments.

To understand where a single score sits on the bell curve, see our guides to what counts as a good IQ score, an IQ of 115, 120 and 130.

How an IQ test works

A professional IQ assessment usually follows the same steps:

1. A qualified examiner gives the test one-to-one. Tests such as the WAIS-5 can only be bought and used by professionals with the right training, usually psychologists. Increasingly, the test is given on a tablet rather than on paper.
2. Each subtest adapts to you. Subtests start at a level suited to your age and stop after a set number of mistakes. You are not expected to answer everything, and most people find the later items difficult.
3. Raw scores become standard scores. The number of points you earn on each subtest is converted, using tables for your age group, into scaled scores and then into index scores and a Full Scale IQ. Our guide to how IQ is calculated shows exactly how.
4. The psychologist interprets the results. The scores are considered alongside your background, education, health and the reason for the assessment, usually in a written report.

How long does an IQ test take?

The core WAIS-5 takes about 45 minutes for the seven subtests that make up the Full Scale IQ, and about 60 minutes for all 10 primary subtests. The whole appointment is usually longer, because it often includes an interview, breaks and sometimes other tests, such as memory or attainment tests. Children's tests take a similar amount of time.

Online IQ tests vary widely. Ours, the IQScore cognitive assessment, has a 25-minute limit.

Types of IQ tests

There are several well-established IQ tests. Which one is used depends mainly on the person's age and the reason for testing.

Scores from different tests are not always directly comparable. Some older tests use a different scale, so the same ability can produce different numbers, as our guide to how IQ is calculated explains.

What are IQ tests used for?

• Education. Educational psychologists use IQ tests to understand why a child is struggling, to identify specific learning difficulties and to decide on support. They are also used, alongside other evidence, to identify gifted pupils.
• Diagnosis of intellectual disability. Diagnosis requires both significantly below-average intellectual ability, typically an IQ around 70 or lower, allowing for measurement error, and difficulties with everyday adaptive skills. An IQ score alone is never enough.
• Health and neuropsychology. IQ tests help assess changes in thinking after a brain injury, stroke or illness, and track them over time.
• Research. Researchers use IQ tests to study how thinking develops, ages and relates to health, education and life outcomes.
• Work and legal settings. Some employers use shorter cognitive ability tests in recruitment, and IQ assessments are sometimes used in court when a person's mental capacity is in question.
• Membership of high-IQ societies. Mensa accepts scores from approved, supervised tests at or above the 98th percentile.

What does an IQ score predict?

IQ is one of the most studied measures in psychology. On average, it is linked with school performance: a major review by the American Psychological Association in 1996 found a correlation of about 0.5 with school grades. IQ is also linked with job performance, especially in complex jobs, although a 2022 re-analysis by Sackett and colleagues suggests the link is weaker than older studies claimed. These are averages across large groups. For any individual, effort, opportunity, health and interests matter a great deal.

What IQ tests don't measure

An IQ test measures a specific set of reasoning abilities. It does not measure:

• Creativity: coming up with original ideas and new ways of doing things.
• Emotional and social skills: understanding people, managing relationships and working in a team.
• Motivation and character: persistence, curiosity, honesty and reliability.
• Knowledge and expertise: what you have learnt about a subject or trade over years of experience.
• Practical skills and wisdom: good judgement in real situations, which grows with experience.

How accurate are IQ tests?

Professional IQ tests are among the most reliable tests in psychology, and taking one again usually gives a similar score. Even so, every score comes with a margin of error, which is why reports give a range. In Pearson's published sample report, a Full Scale IQ of 111 comes with a 95% confidence range of 106 to 116.

Scores can also be affected by tiredness, anxiety, illness, language and familiarity with the test. Taking a test again soon afterwards raises the score through practice alone. Online tests add further problems, which we cover in our guide to whether online IQ tests are accurate.

How do I find out my IQ?

• For an official score, book an assessment with a qualified psychologist, such as a clinical, educational or occupational psychologist. They will use a test like the WAIS-5 and give you a written report. Private assessments are usually paid for, so ask about the cost and what the report includes before booking.
• For a child, start with the school's special educational needs coordinator (SENCo) or the school's educational psychology service if you have concerns about learning.
• To join Mensa, you can take Mensa's own supervised test or submit a score from an approved professional test.
• For a free estimate, try a well-designed online test. It cannot replace a professional assessment, but it can give you a rough idea and help you practise reasoning.

Frequently asked questions

IQScore tests and guides are for education and entertainment. Scores are estimates and are not a clinical or diagnostic result. If you have concerns about memory, attention or learning, please speak to a qualified professional.