Ratio IQ vs deviation IQ
Deviation IQ, used by every modern test, is just distance from your age group's average in standard deviations: 150 means +3.33 SD. Ratio IQ, the old childhood formula, is mental age ÷ age × 100. It produced huge numbers when a young child performed like a much older one, and inflated badly at the top. Try the old formula.
On the original Stanford-Binet and the classifications that dominated the 20th century, the 140–160 region was routinely labelled genius or near genius. Terman, whose 1916 Stanford-Binet popularised IQ in America, used cut-offs here to select his longitudinal study's children.
"Genius" implies creative eminence and lasting achievement, which no test can measure, and it set up an expectation that high scorers would all become world-historical figures. Modern Wechsler scales stop at descriptive bands like Very Superior or Extremely High; gifted-education research uses highly gifted (145+) and profoundly gifted (160+).
How many people score 150+ in…
Answer every hard item, and the test can't tell 150 from 165
Many tests are only well normed to about +2 to +2.7 SD (130–140). Above that, scores lean on the assumption that the curve stays perfectly normal, and a standard test has a finite number of hard items. Extended-norm and high-ceiling tests exist precisely to separate people in this range.
Tap a claim to check it
A documented 150 from a properly administered modern test means far more than any of the legends.
Ability keeps predicting, past where people assume it maxes out
SMPY, tracked by Lubinski and Benbow for over 40 years, found that even within the top 1%, the top quarter went on to far more patents, doctorates and tenure than the bottom quarter. Wai's analyses find elite achievers drawn overwhelmingly from the extreme right tail.
Which number doesn't belong with the others?
Percentiles, rarities and counts are computed from a normal distribution (mean 100, SD 15); population figures are rounded. The ceiling chart is a toy model. Terman, Cox, Hawking, SMPY and Wai points summarise published accounts. The live page's sample sequence duplicated another page's, so this page uses its own item.