# IQ: Scores, Scales and What They Really Measure

> IQ explained: what a score means, how the scale works (mean 100, SD 15), what IQ tests measure and miss, and why how you decide matters more than the number.

Canonical: https://mentarium.io/iq.md

IQ · 6 guides

> **IQ** (intelligence quotient) is a score from a standardized test that shows how a person’s performance on reasoning, memory and problem-solving tasks compares with others their age. Modern tests set the average at 100 with a standard deviation of 15, so about two thirds of people score between 85 and 115.

## Every guide in the library

[Average IQ in the USAThe average IQ in the USA is 100 by design. The most widely used IQ tests, the Wechsler scales and the Stanford-Binet, are normed on large samples built to match the US census, and scores are converted so that the middle of each US age group lands on 100, with a standard deviation of 15.](https://mentarium.io/iq/average-iq-usa) [IQ Scale & Ranges Explained (With Chart)The IQ scale is a standard score scale with a mean of 100 and a standard deviation of 15 on modern tests such as the Wechsler scales and the Stanford-Binet 5. Scores from 90 to 109 are labeled average; about 68% of people score 85 to 115 and about 95% score 70 to 130.](https://mentarium.io/iq/iq-scale) [IQ Test ScoresAn IQ test score is an estimate of where you rank among people your age on a set of reasoning, memory and speed tasks, on a scale with a mean of 100 and a standard deviation of 15. Because every test has measurement error, a score is best read as a range, usually about 5 points either side.](https://mentarium.io/iq/iq-test-scores) [What Is an IQ Test? Definition, History & What It MeasuresAn IQ test is a standardized set of tasks (reasoning, vocabulary, memory, processing speed) that compares your performance with a representative sample of people your age. Modern tests convert the result to a deviation score with a mean of 100 and a standard deviation of 15, called the intelligence quotient, or IQ.](https://mentarium.io/iq/what-is-an-iq-test) [What Is the Average IQ? (By Age, Country & Job)The average IQ is 100 by definition. Modern IQ tests are normed so that the middle score of a representative sample of people your age is set to 100, with a standard deviation of 15. About two thirds of people score between 85 and 115, and about 95% between 70 and 130.](https://mentarium.io/iq/average-iq) [What Was Einstein's IQ? The Real AnswerEinstein's IQ was never measured. Albert Einstein (1879–1955) never took an IQ test, and modern intelligence tests barely existed when he did his most famous work. The widely quoted figure of 160 is a modern estimate with no basis in any test result.](https://mentarium.io/iq/einstein-iq) [Free IQ practice test30 questions, 20 minutes, scored instantly, no sign-up and no paywall.](https://mentarium.io/iq/test)

## What is IQ?

IQ, short for intelligence quotient, is a score that compares your performance on a standardized set of mental tasks with the performance of other people your age. It is a relative measure: a score of 100 means you performed at the average for your age group, not that you got 100 questions right.

The first practical intelligence test came from Alfred Binet and Théodore Simon in France in 1905. They were asked to help identify schoolchildren who needed extra support, and they designed tasks that estimated a child’s “mental age.” The German psychologist William Stern proposed in 1912 dividing mental age by chronological age, giving a quotient. Lewis Terman at Stanford adapted Binet’s test for the US in 1916 (the Stanford-Binet) and multiplied the quotient by 100, which is where the familiar scale started.

Modern tests no longer use that division. David Wechsler, whose tests are among the most widely used today, introduced the “deviation IQ”: your score shows how far you are from the average of a large reference sample of people your age, measured in standard deviations. That is the method nearly all major tests use now. For how tests are built and given, see [what is an IQ test](https://mentarium.io/iq/what-is-an-iq-test).

## How the IQ scale works

The IQ scale is built so that the average is 100 and the standard deviation is 15. Scores follow a bell curve: most people cluster near the middle and fewer appear as you move toward either end. The full breakdown of ranges and labels is on the [IQ scale](https://mentarium.io/iq/iq-scale) page.

| IQ range | Distance from average | Share of people (approx.) |
|---|---|---|
| 130 and above | 2+ SD above | About 2% |
| 115 to 129 | 1 to 2 SD above | About 14% |
| 85 to 114 | Within 1 SD | About 68% |
| 70 to 84 | 1 to 2 SD below | About 14% |
| Below 70 | 2+ SD below | About 2% |

These shares come from the mathematics of the normal distribution, not from any one survey. A few things follow from the design:

- **100 is average by definition.** Tests are re-normed periodically so that the reference group averages 100.
- **Different tests label ranges differently.** One test may call 120 to 129 “superior,” another “high average” to “very high.” Labels are conventions, not facts about people.
- **Small differences mean little.** Every test has measurement error, often several points either way. A 104 and a 109 are not meaningfully different results.
- **Some older or online tests use other scales.** A few use a standard deviation of 16 or 24, which makes the same performance look higher. Always check which scale a number is on.

What one particular number means for you, from 85 to 145, is covered in [IQ test scores](https://mentarium.io/iq/iq-test-scores).

## What is the average IQ?

The average IQ is 100, because tests are designed that way. The more interesting questions are about how averages compare across time and groups. The [average IQ](https://mentarium.io/iq/average-iq) page covers averages by age and the Flynn effect: the political scientist James Flynn documented that raw scores on IQ tests rose substantially across the twentieth century in many countries, which is why tests have to be re-normed.

For the US specifically, see [average IQ in the USA](https://mentarium.io/iq/average-iq-usa). A caution that applies to every country comparison: international average IQ figures come from datasets that are heavily contested, built from samples of very uneven quality and size. Treat country rankings with a lot of skepticism.

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## What IQ tests measure

Most modern IQ tests measure several kinds of ability and combine them into one score. A typical full-scale test includes:

- **Verbal comprehension:** vocabulary, understanding similarities between concepts, general knowledge.
- **Perceptual or fluid reasoning:** spotting patterns, completing matrices, solving novel problems.
- **Working memory:** holding and manipulating information, such as repeating digit sequences backward.
- **Processing speed:** how quickly and accurately you complete simple visual tasks.

People who do well on one of these tend to do somewhat well on the others. In 1904, Charles Spearman proposed a general factor, “g,” to explain that pattern. Most psychologists today accept that IQ tests capture something real and broad, and that scores are associated with outcomes like school performance. They also note that the association is far from perfect, and that many other factors matter as much or more.

## What IQ tests don’t measure

An IQ score leaves out a lot that matters for how life goes:

- **Judgment and decision quality.** Knowing how to weigh options, spot a bad assumption or resist a bias is not what the test asks.
- **Rationality.** The psychologist Keith Stanovich has argued that rational thinking is a distinct set of skills from intelligence, and that high-IQ people show many of the same biases as everyone else.
- **Creativity, curiosity and persistence.** None of these is scored.
- **Knowledge and expertise in a field.** A test samples general reasoning, not what you know about medicine or engineering.
- **Character.** Honesty, kindness and reliability are invisible to an IQ test.

Scores can also be affected by things unrelated to ability: sleep, anxiety, familiarity with the test format, language, and the conditions of testing.

## Online tests vs clinical tests

There is a big difference between a clinical IQ assessment and a test you take online.

|  | Clinical IQ test | Online or practice test |
|---|---|---|
| Who gives it | A trained psychologist, one to one | Nobody: you take it alone |
| Norms | Large, carefully selected reference samples | Usually unknown or informal |
| Length | Often an hour or more, several subtests | Usually 10 to 40 minutes |
| Use | Diagnosis, educational planning, research | Curiosity and practice |

Our free [IQ test](https://mentarium.io/iq/test) is a practice test. It is designed to be fair and interesting, and it gives you an estimate on the standard scale, but it is not a clinical assessment and shouldn’t be used as one.

## Famous IQs and myths

Claims about the IQs of famous people are mostly fiction. Einstein never took an IQ test; the figures that circulate (often 160) are guesses. The [Einstein IQ](https://mentarium.io/iq/einstein-iq) page explains where the numbers come from and why they don’t hold up. The same applies to most historical figures: IQ tests didn’t exist for most of history, and estimating a score from someone’s biography isn’t measurement.

Other common myths:

- **“IQ is fixed from birth.”** Scores are fairly stable in adulthood, but they are influenced by environment, education and health, and population averages have shifted over decades.
- **“A high IQ guarantees success.”** It helps with some things. It guarantees nothing.
- **“Online IQ tests are as good as real ones.”** They aren’t.

## How to think about your own score

If you have an IQ score, from a clinical assessment or a practice test, a few rules keep it in proportion.

1. **Check the scale.** Confirm the test uses a standard deviation of 15. A “140” on a scale with a larger standard deviation is not the same as 140 on a Wechsler-style test.
2. **Think in ranges, not points.** Treat your score as a band of several points either way. Reputable clinical reports often give a confidence interval for exactly this reason.
3. **Remember the conditions.** A bad night’s sleep, a noisy room or test anxiety can lower a score. Familiarity with puzzle formats can raise one.
4. **Separate the score from your worth.** An IQ score describes performance on certain tasks. It says nothing about your character, your values or how much you can learn.
5. **Use it as a starting point, not a ceiling.** Whatever your number, the habits that improve your decisions are available to you.

If you want to understand one specific number, the [IQ test scores](https://mentarium.io/iq/iq-test-scores) page walks through what common scores mean and don’t mean.

## Your IQ is one input. How you decide matters more

Your IQ is one input. How you decide matters more. A high score helps you follow complex arguments and learn quickly. It doesn’t stop you from falling for [confirmation bias](https://mentarium.io/biases/confirmation-bias), anchoring on the first number you hear, or making a big decision without asking what could go wrong. Research on rationality, such as Stanovich’s, suggests intelligence and good judgment are related but far from the same thing.

The good news is that judgment is more trainable than IQ. Two places to start:

- **[Critical thinking](https://mentarium.io/critical-thinking):** the habit of judging claims on evidence and reasoning, including your own.
- **[Mental models](https://mentarium.io/mental-models):** compact tools like [inversion](https://mentarium.io/mental-models/inversion) and [second-order thinking](https://mentarium.io/mental-models/second-order-thinking) that help you see a problem from several angles before you choose.

Take the [IQ test](https://mentarium.io/iq/test) if you are curious about your number. Then spend more time on how you use it.

## The Mentarium take

IQ is one of the most studied measures in psychology, and it does capture something real. It is also one of the most overinterpreted. People treat a single number as a verdict on their worth, their potential or their intelligence in every sense of the word, and it is none of those.

Our view: an IQ score is a useful description of how you performed on a particular set of reasoning tasks, on a particular day, compared with a particular group. That is all. What you do with your mind (how you frame problems, check your assumptions and learn from your decisions) shapes your life far more, and unlike the score, it is something you can deliberately improve.

## FAQ

### What is a normal IQ score?

On modern tests, the average is set at 100. About two thirds of people score between 85 and 115, which is usually described as the average range. About 95% score between 70 and 130.

### What does an IQ test actually measure?

IQ tests measure performance on a set of cognitive tasks: verbal reasoning, pattern and spatial reasoning, working memory and processing speed. Scores on these tasks tend to correlate, and that shared factor is what most psychologists mean by general intelligence. Tests don't measure creativity, wisdom, character or judgment directly.

### Is an online IQ test accurate?

An online test can give a rough, informal estimate at best. Clinical IQ tests are administered one to one by a trained psychologist, use carefully normed samples and take an hour or more. Free online tests, including practice tests like ours, aren't clinical and shouldn't be used for any official purpose.

### Can you increase your IQ?

Practice on test-style puzzles can raise your score on similar tests, but that mostly reflects familiarity, not a broader change in ability. Education is associated with higher scores, and population averages rose over the twentieth century (the Flynn effect). Large, lasting gains for an adult from training programs are not well supported.

### What was Einstein's IQ?

Nobody knows. Einstein never took an IQ test. Figures like 160 that circulate online are guesses, not measurements.

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