Where famous IQ numbers come from

1. A 1926 estimate from biographies. Psychologist Catharine Cox compared what biographies said 301 eminent people could do at each age with what an average child could do, and converted that into an IQ. Nobody was tested. She rated childhood (to 17) and young adulthood (17 to 26) separately, then corrected for gaps in the record. Newton's 190, Napoleon's 145 and Mozart's 165 are all her corrected figures, and her study only covers people born between 1450 and 1850.

2. A reported school or admissions test. A few people have a real number from a real test, such as John F. Kennedy's reported 119 on a school intelligence test. Even then it is a single group test from decades ago, with wide error and old norms.

3. No source. Round numbers such as Einstein's and Hawking's 160, Bezos's 150+ and Leonardo's 200 to 220 appear on lists that cite no test, study or method. Some are conversions from an SAT score, which cannot separate very high scorers.

• Ask who measured it. If the answer is not a named test, date and person, treat the number as decoration.
• Old numbers use an old scale. Cox's corrected figures are not on today's mean-100, standard-deviation-15 scale. See the Flynn effect.
• A conversion is not a measurement. Turning an SAT score into an IQ gives a rough idea at best. See SAT to IQ.
• Matching numbers are a warning. When two very different people share the same round number, it was probably borrowed.

Want your own number from a real test? Take the free IQ test, or see how the tests compare in best IQ tests. All the profiles are in famous IQs.

The Cox figures are the corrected estimates (Table 12A) as tabulated in secondary sources; childhood and young adult figures are shown only where a secondary source reports them. The Flynn adjustment subtracts about 22 points, the rough figure one secondary tabulation uses, and rounds to the nearest 5. The traced claims use the same facts as each person's history profile. Where we could not find a source, we say so instead of guessing. Last checked 22 October 2026.