How IQ Tests Work: What an IQ Test Measures and How IQ Is Calculated

An IQ test measures reasoning ability, and IQ is calculated by comparing your performance on a standardized set of problems to a large, representative sample of people your age. You never receive a score of "42 out of 60" — instead, your raw performance is converted into a position on a bell curve where the average is fixed at 100 and the standard deviation is 15. An IQ score is not a measurement of your brain in isolation; it is a statement about where you stand relative to everyone else.

What does an IQ test measure?

An IQ test measures reasoning ability — how well you solve novel problems, work with language, hold information in mind and process it quickly — and reports the result relative to other people your age. It does not measure knowledge, creativity, effort or character.

Full-scale batteries such as the Wechsler scales report the abilities they sample as separate index scores. In broad terms, what an IQ test measures breaks into five areas:

• Fluid reasoning: solving unfamiliar problems by logic alone, with no prior training to fall back on.
• Verbal comprehension: vocabulary, analogies and reasoning expressed in language.
• Visual-spatial ability: seeing how shapes relate, rotate and fit together.
• Working memory: holding several pieces of information in mind and manipulating them.
• Processing speed: how quickly and accurately you get through simple, repetitive tasks.

Not every test covers all five. Ours is a matrix-reasoning test, so it measures fluid and visual-spatial reasoning rather than the full set — see our methodology for exactly what it does and does not sample.

Modern tests don't rely on a single question type. They sample several distinct abilities, because intelligence research consistently finds that performance across very different tasks is correlated — the statistical core known as the general factor, or g. The main question families are:

Matrix reasoning

You see a grid of abstract shapes with one cell missing and must pick the option that completes the pattern. This is the Raven's Progressive Matrices format, and it targets fluid reasoning — solving novel problems without relying on learned knowledge. It is the backbone of most serious modern tests, including ours. If you want concrete practice-style examples, see our IQ test questions guide.

Verbal reasoning

Vocabulary, analogies ("hand is to glove as foot is to…"), similarities and comprehension questions. These tap crystallized intelligence — accumulated knowledge and the ability to reason with language.

Working memory

Holding and manipulating information in your head: repeating digit sequences backwards, mental arithmetic, remembering positions in a sequence. Working memory is one of the strongest single correlates of overall reasoning ability.

Processing speed

Simple tasks done under tight time pressure — matching symbols, scanning for targets. Individually trivial, but the speed and accuracy with which you complete them is surprisingly informative about overall cognitive efficiency.

Why matrix reasoning is considered culture-reduced

Verbal questions have an obvious weakness: they depend on the language you grew up speaking and the education you received. A brilliant reasoner tested in their second language will underperform. Matrix puzzles sidestep much of this — they use no words, no arithmetic notation and no culturally specific knowledge. That's why researchers call them culture-reduced (not culture-free — test familiarity and schooling still help), and why matrix formats are preferred when testing across countries or online.

How IQ is measured and calculated, step by step

IQ is measured by comparison, not by counting. Nothing about your answers has a fixed value in points; the number you receive is calculated from where your raw performance sits inside a reference group. Here is the machinery that turns puzzle answers into an IQ:

• Step 1 — the norming sample. Before a test is published, it is administered to a large sample chosen to represent the population by age, education and region. This sample defines what "normal" performance looks like.
• Step 2 — your raw score. When you take the test, your answers produce a raw score — typically the number correct, sometimes weighted by item difficulty.
• Step 3 — your position in the distribution. Your raw score is located within the norming sample's distribution for your age group. Scoring exactly at the median puts you at the 50th percentile.
• Step 4 — conversion to IQ. That percentile is mapped onto a normal curve with mean 100 and standard deviation 15. The 84th percentile becomes 115; the 98th becomes 130.

This is called deviation scoring, and it is why the average IQ is always 100 by construction, why about 68% of people score between 85 and 115, and why every score has a direct percentile equivalent. Because the score comes from your distance from the average rather than from a ratio, this kind of score is properly called a deviation IQ. The original intelligence quotient really was a quotient — mental age divided by chronological age, multiplied by 100 — but that arithmetic was abandoned decades ago because it breaks down in adulthood, where mental age stops climbing with the calendar. Only the name survives. For what the resulting numbers mean once they are calculated, see the IQ score chart.

Two consequences of this design are worth spelling out. First, an IQ score only means something relative to its norming sample: a score from a test normed in 1985 is not directly comparable to one normed last year, because raw performance drifted upward across the 20th century (the Flynn effect) and publishers must periodically re-norm. Second, the quality of the norms is the quality of the test. A beautifully designed puzzle set normed on a small, self-selected sample — the situation with many free online quizzes — produces numbers that look like IQ scores but aren't anchored to anything. This is exactly why Mensa accepts only specific supervised tests rather than any score you arrive with.

Your score is a range, not a point

No test measures perfectly. If you took the same test twice, your scores would differ slightly — attention drifts, some items happen to suit you, some don't. Psychometricians quantify this with the standard error of measurement (SEM) — the scale's standard deviation of 15 multiplied by the square root of one minus the test's reliability. At a reliability of .95 that is 3.4 points, which puts the 95% confidence interval at roughly ±5 to ±7 points. In practice, a measured score of 110 is best read as a band of about 103–117 rather than a fixed number. This is why clinicians report confidence intervals rather than bare numbers, and why arguing over a 3-point difference between two people is statistically meaningless. The full arithmetic, and what happens to it on a less reliable test, is worked out in are IQ tests accurate.

Retesting adds its own wrinkle: taking the same or a similar test again within months typically raises the score a few points purely through familiarity — a practice effect, not a genuine gain in ability. Serious assessments handle this with alternate forms and minimum retest intervals; serious readers handle it by treating any single sitting as one noisy sample of a stable underlying level.

One clarification belongs here, because it is constantly conflated: asking whether a test gives consistent results and asking whether it measures anything that matters are two different questions. Major IQ tests do well on both — they are among the most reliable measurements in psychology, and scores predict educational attainment and job performance better than any other single psychological measure, though probabilistically rather than as destiny. We take that apart properly, with the numbers, in are IQ tests accurate.

What an IQ test does not measure

An honest account has to include the boundaries. IQ tests do not measure creativity (generating original ideas is a different skill from converging on one correct answer), emotional intelligence (reading and managing emotions in yourself and others — see the difference between IQ and EQ), practical judgment, motivation, curiosity or character. A high scorer can make terrible decisions; an average scorer can build an exceptional career. If you want to raise the abilities the tests do capture, see what the evidence supports in how to increase your IQ.

Those boundaries are exactly what Howard Gardner's theory of multiple intelligences was written to argue about: whether musical, bodily and interpersonal abilities deserve the name intelligence at all, or whether they are talents that sit outside it. That argument is still live, and we set out both sides in the types of intelligence.

What is the Wechsler Adult Intelligence Scale (WAIS)?

The Wechsler Adult Intelligence Scale (WAIS) is the most widely used measure of adult intelligence — an individually administered clinical instrument given one-on-one by a qualified professional to people aged 16 to 90, reporting a Full Scale IQ plus separate index scores for the abilities it samples. It is the instrument most people have in mind when they say "a real IQ test", and it is the reason the mean-100, SD-15 metric is the scale every other test is read against.

The scale is named for David Wechsler, and it is where the modern metric described above comes from: deviation scoring was his answer to the problem of measuring adult intelligence, and the mean of 100 with a standard deviation of 15 is the Wechsler convention that nearly every other test now follows. The children's version is the Wechsler Intelligence Scale for Children (WISC). For what the resulting numbers mean, see the IQ scale and score chart.

What the WAIS measures, and how the WAIS-IV and WAIS-5 differ

Two editions are currently in circulation, and they organize the same raw material differently:

• WAIS-IV (2008): covers ages 16 to 90, takes 60–90 minutes for its ten core subtests, and reports four index scores — Verbal Comprehension, Perceptual Reasoning, Working Memory and Processing Speed.
• WAIS-5 (2024): covers the same age range and reports five primary indexes — Verbal Comprehension, Visual Spatial, Fluid Reasoning, Working Memory and Processing Speed. Where the WAIS-IV reported a single Perceptual Reasoning index, the WAIS-5 reports Visual Spatial and Fluid Reasoning separately. Its Full Scale IQ comes from seven subtests in about 45 minutes; all ten primary index subtests take about 60.

Both report the Full Scale IQ and each index on the same metric this page has been describing — mean 100, standard deviation 15 — while individual subtests use a separate scale with a mean of 10 and a standard deviation of 3. A WAIS result therefore reads on exactly the same IQ score chart as any other deviation-scored test: 130 on the WAIS is the same rank as 130 anywhere else, because both describe the same distance above the same average.

Can you take the WAIS online?

No. The WAIS is not published as a self-administered online test in any edition. Pearson restricts purchase to what it classifies as Qualification Level C — in practice a doctorate in psychology, education or a closely related field with formal training in clinical assessment, or an equivalent state licence, certification or professional membership. It is, in Pearson's own words, "an individually administered clinical instrument": every edition is given by a qualified examiner who presents the materials, times the subtests and records the responses as the session runs. Some of that can happen over video — Pearson publishes telepractice guidance for both editions, and says the WAIS-5 Nonmotor Index "can be easily applied in remote testing situations" — but remote still means an examiner administering the test live. There is no self-administered version, so a site offering a "free online WAIS" is not administering the WAIS.

That distinction matters for reading any online result, ours included. This site's test is a matrix-reasoning estimate — not a Wechsler scale, and not a substitute for one. It samples a narrower set of abilities, and it is not a clinical, educational or diagnostic instrument. If you need a score that carries formal weight, the route is a licensed psychologist. The next section sets out what an online estimate can and cannot tell you.

To be clear about the relationship: IQ Revealed is not affiliated with, endorsed by or connected to Pearson, Mensa or any publisher of the tests described here, and does not administer, score or prepare anyone for them. They are named here because a reader asking how IQ tests work deserves to know what the professionally administered ones actually are.

Online estimates vs clinical administration

A clinical IQ assessment — typically the Wechsler Adult Intelligence Scale (WAIS) — is administered one-on-one by a licensed psychologist over 60–90 minutes, covers ten or more subtests, and produces a formally valid score usable for diagnosis, schooling decisions or legal purposes. It also costs several hundred dollars.

Online tests, including ours, are estimates. Ours draws on the same kind of matrix-reasoning material a clinical battery uses, but it is not standardized on a norming sample, it cannot control your environment, it cannot verify your effort, and it cannot diagnose anything. Treat any online score as a rough indication with a wide error band, not a clinical fact. IQ tests are also just one member of a broader family of assessments used in hiring and education; for a direct accuracy-focused breakdown, read are IQ tests accurate. Then see our guide to cognitive ability tests for how the pieces fit together, and the IQ scale for what each score range actually means. And because the question comes up constantly: what an IQ test measures is not what a personality test measures — see why no personality type is the smartest.

Conditions are also the subject of one of the best-known claims about testing: stereotype threat, whose research record is more contested than most accounts admit.