Estimate, not a test
François AragoPhysicist and astronomer
Cox rated him 165 for ages 17 to 26, 1 point below 166. Cox's childhood rating for him was 145.
IQ 166: rarity and the "optimum" question
An IQ of 166 is higher than about 99.99945% of people, roughly 1 in 184,756. It is far above what Leta Hollingworth, a pioneer of gifted education, called the "optimum" range for a happy, well-adjusted childhood, which she put at about 125 to 155.
99.99945thpercentile
1 in 184,756score 166 or higher
Exceptionally giftedlevel of giftedness
166IQ scoreTop 0.00054%
How far out on the bell curve is 166?
Plot 166 on the bell curve and it lands 4.4 standard deviations, or 66 points, to the right of the average. The area beyond it, coloured orange below, holds only 0.00054% of people, too thin to see without zooming in.
166 is more than four standard deviations above average: roughly one person in every 185,000.
What makes 166 different
Hollingworth studied gifted children in New York from 1916 until her death in 1939. Her conclusion was not that higher is always better. Children well above average but not extremely so, she wrote, are "enough more intelligent than the average to win the confidence of large numbers of their fellows" and have enough peers to find "mutual esteem and understanding".
At 166, a child is beyond that range. Hollingworth's scores came from the older Stanford-Binet and aren't directly comparable with modern ones, but her central point still guides gifted education today: the further a child is from their classmates, the more deliberately adults need to help them find intellectual peers.
How many people have an IQ of 166?
To meet one person scoring 166 or above, you would need, on average, a crowd of 184,756. Here is that crowd, built up step by step.
A crowd of 184,756 people
184,756
Every dot stands for a person. Only the orange one, one in the whole crowd, would be expected to reach 166.
People scoring 166 or higher, by population
| Worldwide (8.2 billion people) | about 44,500 |
| India | about 7,920 |
| United States | about 1,850 |
| United Kingdom | about 376 |
| Canada | about 225 |
| Australia | about 149 |
Population: World Bank, total population, 2025. Counts assume the same bell curve in every country and are rounded. Real tests can't sort people this finely, as the next sections explain.
Which high-IQ societies accept an IQ of 166?
Each society below admits a set top slice of the population and lists the score that matches it on the Wechsler adult scale. With a supervised result of 166, you would meet 5 of the 6 bars; the next, Mega Society, needs about 171.
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MensaTop 2% (98th percentile) on an approved, supervised test130met
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IntertelTop 1% (99th percentile); lists a Wechsler full-scale IQ of 135135met
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Triple Nine Society99.9th percentile; lists a WAIS full-scale IQ of 146146met
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International Society for Philosophical Enquiry99.9th percentile; lists a WAIS-III or WAIS-IV full-scale IQ of 146146met
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Prometheus Society1 in 30,000 (99.997th percentile), four standard deviations above average160met
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Mega SocietyOne in a million, beyond the range of standard tests171not met
Scores for Mensa, Intertel, Triple Nine and ISPE are the Wechsler figures those societies list or that match their percentile. Prometheus and Mega give only a rarity; the scores shown are the matching points on the standard scale. Prometheus says no test currently being given is approved for its entry. Online test results are not accepted by any of them.
Can an IQ test measure 166?
A score of 166 is 6 points past the ceiling of the main clinical tests, which stop at 160. The bars show the highest full-scale result each test can give; only the extended scales, used mainly with exceptionally able children, can report 166.
Behind every score is a norm sample: for the WAIS-IV, 2,200 adults. The bell curve predicts about 0.01 of them at 166 or above, far less than one person, so no standard test has ever compared anyone with real 166 scorers. Extended norms are built from children who reach the ceiling of the standard test, and their scores rest on that projection.
Add the usual margin of error, about five points either way, and a result of 166 really means somewhere near 161 to 171. Very few people have ever been tested this high, so even extended scales are working near the limit of their evidence. No online test can pin down a score like this, ours included. What online tests can and can't tell you.
Sources: WAIS-IV range and norm sample from Canivez (2010), Mental Measurements Yearbook review; Stanford-Binet 5 and its Extended IQ from PRO-ED; WISC-V extended norms from Pearson Technical Report #6 (2019). Striped bars are extended scales, used only when a person hits the normal ceiling.
Is 166 the same on every IQ scale?
IQ tests don't all use the same yardstick. A scale with a larger standard deviation turns the same rank into a bigger number, especially this far above average.
166standard scale (SD 15), used by Wechsler tests and on this page
170older Stanford-Binet scale (SD 16)
206Cattell scale (SD 24), used by some older and online tests
Turn it around: if a test using the Cattell scale reports 166, the standard-scale equivalent is just 141. From an SD 16 test, 166 converts to about 162. Check the scale before comparing any high score. IQ standard deviations explained.
Historical figures rated at about 166
The figures below are not test scores. In 1926 the psychologist Catharine Cox rated 301 eminent people from records of their youth, giving each a childhood estimate and a second one for ages 17 to 26.
Samuel Taylor ColeridgePoet and critic
Cox rated him 165 for ages 17 to 26, 1 point below 166. Cox's childhood rating for him was 175.
Thomas Babington MacaulayHistorian and politician
Cox rated him 165 for ages 17 to 26, 1 point below 166. Cox's childhood rating for him was 180.
Source: Cox, C. M. (1926), Genetic Studies of Genius, Vol. II: The Early Mental Traits of Three Hundred Geniuses, Stanford University Press. Cox stressed that thin records pull estimates down. Read more in where the historical genius IQ estimates came from.
Hollingworth's idea of "optimum intelligence"
"There is a certain restricted portion of the total range of intelligence which is most favorable to the development of successful and well-rounded personality," Hollingworth wrote. "This limited range appears to be somewhere between 125 and 155 IQ."
Above it, she argued, children face "special problems of development which are correlated with personal isolation", because they are "too infrequent to find many congenial companions". Her answer was not to hold such children back but to place them with others of similar ability.
Source: Hollingworth, L. S. (1942), Children Above 180 IQ Stanford-Binet: Origin and Development, World Book Company (Project Gutenberg edition).
What does an IQ of 166 mean?
An IQ of 166 means a reasoning level shared by about five people in a million of the same age. In practical terms for a child, it usually means a school curriculum moving far too slowly, which psychologists address with acceleration, mentoring or specialist programmes rather than more of the same work.
Where 166 falls among the levels of giftedness
115–129Mildly gifted
130–144Moderately gifted
145–159Highly gifted
160–179Exceptionally gifted
180+Profoundly gifted
Levels and ranges from Gross, M. U. M. (2000), "Exceptionally and Profoundly Gifted Students: An Underserved Population", Understanding Our Gifted. They are a guide for education, not a ranking of people.
How far 166 is from other milestones
20 points above the Triple Nine and ISPE bar (146)a score of 166 is about 200 times rarer than 146
6 points above the ceiling of most professional tests (160)a score of 166 is about 5.9 times rarer than 160
5 points below the Mega Society's one-in-a-million level (171)reaching 171 is about 5 times rarer than 166
14 points below the start of the profoundly gifted band (180)reaching 180 is about 112 times rarer than 166
4.4 standard deviations above averageaverage is 100 and one standard deviation is 15 points
IQ 166 compared with nearby scores
| IQ | Percentile | Rarity | Level |
|---|---|---|---|
| 162 | 99.9982nd | 1 in 55,938 | Exceptionally gifted |
| 164 | 99.999th | 1 in 100,799 | Exceptionally gifted |
| 166 | 99.99945th | 1 in 184,756 | Exceptionally gifted |
| 168 | 99.9997th | 1 in 344,471 | Exceptionally gifted |
| 170 | 99.99984th | 1 in 653,327 | Exceptionally gifted |
166 IQ: common questions
Is 166 a high IQ?
Yes. 166 is a very high IQ: about 1 person in 184,756 scores this high or higher, which puts it at the 99.99945th percentile. It is above the 130 that most definitions use for a high IQ, and at or above the 146 used by the Triple Nine Society for its 99.9th percentile entry.
Is an IQ of 166 good?
Yes, by any measure. 166 is higher than about 100% of people. Remember that a score this high needs a supervised professional test to be confirmed, and that it describes reasoning on a test, not every kind of talent.
Can you join Mensa with an IQ of 166?
Yes. Mensa accepts the top 2% on an approved, supervised test, which is about 130 on the standard scale. A supervised 166 would also meet the bar for Intertel, Triple Nine Society, International Society for Philosophical Enquiry and Prometheus Society. Online test results are not accepted.
What does 166 IQ mean?
It means a result 66 points, or 4.4 standard deviations, above the average for your age. On the levels used by gifted education researchers, 166 is exceptionally gifted (160–179).
Is 166 a genius IQ?
There is no official genius score. Lewis Terman's early Stanford-Binet labels put scores over 140 in a "near genius or genius" group, but modern tests dropped the word. 166 is very rare, yet achievements, not test scores, are what usually earn the word genius.
Is a 166 IQ too high to be happy?
No score decides happiness. Leta Hollingworth found that children far above average often struggled to find peers, and called 125 to 155 the "optimum" range for social adjustment, but she saw the cause as a lack of suitable company, which schools and families can address.
Related: what counts as a good IQ score, the highest IQ in the world, famous people's IQs and the full IQ scale and range chart.
Behind a single score of 166 sit several separate abilities. Read about abstract reasoning, spatial reasoning, verbal reasoning, processing speed and fluid vs crystallized intelligence, or try the free pattern recognition test.
Curious which celebrity IQs near 166 hold up? Read the full stories of Garry Kasparov's IQ, Terence Tao's IQ, Einstein's IQ, Isaac Newton's IQ, Nikola Tesla's IQ, Stephen Hawking's IQ, Bill Gates' IQ and Elon Musk's IQ.
Curious where you'd land?
Our free test takes about 25 minutes and gives an estimated IQ with its percentile. Results go up to 145, so a score like 166 can only be confirmed by a psychologist.
Take the free IQ testPortraits are pencil-style sketches by Assessivo, based on: Samuel Taylor Coleridge after Washington Allston (1814), public domain. Thomas Babington Macaulay after Sir Francis Grant, public domain.