IQ 198

198 is 6.53 standard deviations above the mean. On a bell curve that works out to about 1 in 31 billion people, which is fewer than one person in the entire world population. The bell curve is a model, though, and at this height it is doing most of the work.

Real populations may not follow the bell curve perfectly in the far tails, so rarity figures this extreme are illustrations, not head counts.

None of this means nobody is this able. It means a single number is not a reliable way to describe them.

Most very high numbers you see online come from one of a few sources, and knowing which one produced a 198 tells you how much weight to put on it.

• Ratio IQ. Early childhood tests divided mental age by real age. A 6-year-old solving puzzles like a typical 11.9-year-old got a ratio IQ of 198. Modern deviation IQs do not work this way.
• Historiometric estimates. Researchers such as Catharine Cox (1926) estimated IQs for famous people from biographies. Some of her adjusted estimates went above 200. They are educated guesses, not test results.
• Repetition without a source. Numbers attached to celebrities are often copied from site to site with no test report behind them.

Isaac Newton and Leonardo da Vinci are usually given estimates of 160 or more, and they are among 42 such profiles here. Only 1 goes as high as 198. All are judgements from biographies, not test results.

Estimates this high mostly reflect how extraordinary the achievement was. That is a different thing from how someone would perform on a timed reasoning test.

Scoring 198 or higher is a 0.0000000032% share of everyone. Scaled up to whole populations, that works out as:

Going from 193 to 198 makes a score 8.8 times rarer, and going on to 203 multiplies the rarity by another 9.8. Near 198, each single point adds about 56% to the rarity.

What your 198 could really be. No test is precise this far out. Even a 5-point error band, from 193 to 203, spans a rarity gap of about 86 times, so the exact number matters much less than "very far above average".

Which scale was it on? Score reports do not always say. On the common SD 15 scale your 198 stands as it is. If the report used SD 16 it equals about 192, and if it used SD 24 about 161. The percentile follows the converted number.

Estimates this high are reserved for a small group of scientists, artists and thinkers. These sit near 198. Treat these as informed guesses from biographies rather than results. Each profile sets out what its estimate rests on.

How 198 stacks up against the scores just around it and the round numbers people usually ask about. Each score links to its own page.