Reference
The IQ scale
IQ is a ranking, not a quantity. The scale sets the population average at 100 and spreads scores so that each 15 points is one standard deviation. Here is what every range means.
IQ score ranges
These are the descriptive labels most widely used with modern tests on the SD 15 scale. They are conventions for talking about scores, not diagnoses.
| IQ range | Label | Share of people |
|---|---|---|
| 130 and above | Very high | about 2 in 100 |
| 120–129 | High | about 7 in 100 |
| 110–119 | Above average | about 16 in 100 |
| 90–109 | Average | about 50 in 100 |
| 80–89 | Below average | about 16 in 100 |
| 70–79 | Low | about 7 in 100 |
| Below 70 | Very low | about 2 in 100 |
IQ percentile chart
A percentile says what share of people score lower. An IQ of 115 is at the 84th percentile: higher than 84 in 100.
| IQ | Percentile | Rarity |
|---|---|---|
| 70 | 2 | 1 in 44 score this low or lower |
| 80 | 9 | 1 in 11 score this low or lower |
| 85 | 16 | 1 in 6.3 score this low or lower |
| 90 | 25 | 1 in 4 score this low or lower |
| 95 | 37 | 1 in 2.7 score this low or lower |
| 100 | 50 | 1 in 2 |
| 105 | 63 | 1 in 2.7 score this high or higher |
| 110 | 75 | 1 in 4 score this high or higher |
| 115 | 84 | 1 in 6.3 score this high or higher |
| 120 | 91 | 1 in 11 score this high or higher |
| 125 | 95 | 1 in 20.9 score this high or higher |
| 130 | 98 | 1 in 44 score this high or higher |
| 135 | 99.0 | 1 in 102 score this high or higher |
| 140 | 99.6 | 1 in 261 score this high or higher |
| 145 | 99.9 | 1 in 741 score this high or higher |
How the bell curve works
Scores on a well-built test fall into a bell shape: most people near the middle, fewer toward either end. The scale is defined so that:
- 68% of people score within 15 points of 100 (85 to 115).
- 95% score within 30 points (70 to 130).
- 99.7% score within 45 points (55 to 145).
Because the scale is a ranking, an IQ of 120 is not “20% smarter” than 100. It means a higher position in the queue: ahead of about 91 people in 100 instead of 50.
Why the same person gets different scores
Different scales
Most modern tests use a standard deviation of 15. Some use 16, and the Cattell scale uses 24. The same performance gives 130, 132 or 148 depending on the scale, which is why claimed scores are often not comparable. Use the percentile calculator to convert.
Measurement error
Every test has a margin of error. On a long supervised test it is a few points. On a short online test it is around ten. A result should always be read as a range.
Different abilities
A full assessment combines reasoning, vocabulary, memory and speed. A puzzle-only test measures reasoning alone, so someone strong in one area and weaker in another will score differently on each.
Questions people ask
What is the IQ scale?
A scale that places a test score relative to the population. The average is set at 100 and the standard deviation at 15, so about 68% of people score between 85 and 115 and about 95% between 70 and 130.
What is a normal IQ range?
90 to 109 is usually labelled average and covers about half of all adults. Counting 85 to 115, one standard deviation either side of the mean, covers about two thirds.
What IQ is considered high?
120 to 129 is commonly labelled high or superior, which about 7 in 100 people reach. 130 and above, about 2 in 100, is very high and is the usual threshold for gifted programmes and high-IQ societies.
What is a genius IQ?
There is no official genius score. Older classifications used 140 and above, which roughly 1 person in 260 reaches on the SD 15 scale. Psychologists today avoid the label, because achievement depends on far more than one test score.
Is an IQ of 132 the same on every test?
No. Tests use different standard deviations. 130 on the common SD 15 scale equals 132 on an SD 16 scale and 148 on the SD 24 Cattell scale. Always check which scale a score is on.