What is the average IQ?
The average IQ is 100. That is not a finding, it is a definition. Every major test is deliberately calibrated so the middle of the population lands on exactly that number.
Most measurements describe something out in the world. A thermometer does not decide what a normal temperature should be. IQ works the other way round, and understanding that explains almost everything else about the scale.
Why 100 is not a coincidence
When a test is built, it is given to a large sample chosen to represent the population. Whatever that sample scores becomes the reference. The raw results are then stretched and shifted onto a scale where the middle sits at 100.
The number is assigned, not discovered.
If everyone got better at the questions tomorrow, the average would still be 100 the moment the test was re-normed. Saying the average IQ is 100 is closer to saying a metre is 100 centimetres than to saying the average height is 170cm.
This is also why comparing scores from different tests, or from different decades, needs care. Two people both scoring 120 may have been measured against very different reference groups.
How scores spread around it
The other half of the definition is the standard deviation, set at 15 on modern tests. That fixes how quickly scores become rare as you move away from the middle.
| Range | Distance from mean | Share of people |
|---|---|---|
| 85 to 115 | One SD either side | About 68% |
| 70 to 130 | Two SD either side | About 95% |
| 55 to 145 | Three SD either side | About 99.7% |
Two consequences follow, and both surprise people.
Most people sit near the middle, and that is the design. Two thirds of everyone lands between 85 and 115. Inside that band, small differences move the percentile a lot and mean very little. A 96 and a 108 are, for any practical purpose, the same score. The average range page covers every score in that band individually.
Rarity climbs viciously at the edges. Moving from 100 to 115 puts you past about a third of the population. Moving from 130 to 145 puts you past a much smaller slice, but the number of people remaining above you falls from roughly 1 in 44 to roughly 1 in 741. The mechanics of that are covered in IQ percentiles explained.
The Flynn effect in one paragraph
Through most of the twentieth century, raw scores on IQ tests rose steadily, very roughly three points per decade across many industrialised countries. Because tests get re-normed, the reported average stayed at 100 the whole time. Someone scoring 100 today is answering more questions correctly than someone who scored 100 in 1950. We cover the causes, and the evidence the trend has stalled, in the Flynn effect.
Average IQ by country, and why to be careful
You will find tables ranking nations by average IQ. Treat them with real caution.
The underlying samples vary enormously in quality. Some come from nationally representative studies, others from small convenience samples of students. Translation changes item difficulty. Schooling access, nutrition, and simple familiarity with taking tests all move scores independently of reasoning ability, and those things differ hugely between countries.
The comparisons that survive scrutiny tend to be within-country over time, not between countries at a point in time.
What average does not mean
An average score is a position in a distribution on one kind of task, measured once. It is not a description of a person.
Reasoning ability is real and IQ measures a genuine slice of it. But 100 is where most people live, and most people are competent, skilled and good at things. Reading a midpoint as a disappointment mistakes the scale for a scoreboard.
If you want to see where you actually sit, our free IQ test gives you a score and a percentile in about ten minutes, with nothing gated at the end. You can also see a sample result first if you would rather know what you are getting.
Key takeaways
- The average IQ is 100 by construction. Tests are normed so the population mean lands exactly there.
- The standard deviation of 15 fixes how fast scores get rare as you move from the middle.
- About 68 percent of people score between 85 and 115, and small differences inside that band mean very little.
- Raw performance rose through the twentieth century, but re-norming keeps the reported average at 100.
- National average IQ comparisons are unreliable because sample quality, translation and schooling access vary too much.
- An average score is a position on one task, not a description of a person.