Question
What is the highest possible IQ score?
Short answer
There is no single highest possible IQ. Every test has a ceiling, the top score its items and norms can support, and that ceiling differs from test to test. On a standard deviation 15 scale, 160 is four standard deviations above the mean, a score the bell curve puts at roughly 1 in 32,000 people.
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What a ceiling is
A test can only tell people apart if it has items hard enough to challenge them. Once someone gets nearly every item right, the test has nothing left to measure. The highest score it can then give is its ceiling. Above that, the number reflects the scoring rules more than the person. Our glossary entry on the ceiling effect explains why this matters.
Try one · Quantitative Reasoning
Which number comes next?
5, 10, 17, 26, 37, ?
Tap the option you think is right, or show the answer.
Show the answer
The next number is 50 (option 6).
How to solve it
- The gaps (5, 7, 9, 11) grow by 2 each time, which is the pattern of square numbers.
- Each number is a square number plus 1: 2 × 2 + 1, 3 × 3 + 1, 4 × 4 + 1, 5 × 5 + 1, 6 × 6 + 1.
- So the next number is 7 × 7 + 1 = 50.
That was 1 puzzle. The full test has 25.
How rare the top scores are
Scores follow a bell curve by construction. About 99.7% of people score between 55 and 145 on a scale with standard deviation 15 (the 68-95-99.7 rule). Further out, the numbers thin quickly:
| IQ | About 1 in |
|---|---|
| IQ 145 | 740 |
| IQ 150 | 2,300 |
| IQ 155 | 8,100 |
| IQ 160 | 32,000 |
To place someone reliably at 1 in 32,000, a test would need a norming sample with many people that far out, which is very hard to collect. That is the core reason extreme scores are uncertain.
Error grows at the edges
Even mid-range clinical scores carry a confidence interval, often around plus or minus 5 points at 95% (Wechsler, 2008). Near the ceiling it is wider, because one more or one fewer right answer moves the estimate a long way. On IQ Octopus the reported range around a very high estimate is wider than around one near 100.
Different scales, different tops
Older Stanford-Binet forms used a standard deviation of 16 and the Cattell scale uses 24 (Wikipedia: IQ classification), so the same rarity prints as a bigger number on those tests. A “highest IQ” quoted without its scale tells you little. See what IQ is considered genius for the labels at the top of the scale.
Sources
- IQ classification. Wikipedia. en.wikipedia.org/wiki/IQ_classification
- 68-95-99.7 rule. Wikipedia. en.wikipedia.org/wiki/68%E2%80%9395%E2%80%9399.7_rule
- Wechsler, D. (2008). WAIS-IV Technical and Interpretive Manual. Pearson.