Pick the scale your score is on, then type or drag — the equivalents update live.
Stanford-Binet 5 / Wechsler · SD 15130
Older Stanford-Binet · SD 16132
Cattell · SD 24148
z-score (SDs from mean)+2.00
Free tool · Live
IQ Score Converter
Convert IQ scores between Stanford-Binet 5, older Stanford-Binet, Wechsler, and Cattell scales. All scales share a mean of 100; they differ only in standard deviation.
Different IQ tests use different scoring conventions, and converting between them is a matter of standardising the score on each test’s own normal distribution and re-expressing it in another. The calculator above does the conversion for the four most common conventions.
Why scores differ between scales
All IQ scales are calibrated to the population mean of 100. They differ in their standard deviation: how spread out the scores are. The Stanford-Binet has used SD 15 since 2003 to align with the Wechsler scales. Older Stanford-Binet editions (1960, 1986) used SD 16. The Cattell scale uses SD 24, which spreads scores out more, making the same percentile look like a much higher number.
A score of 148 on Cattell is the same percentile (about 98th) as a score of 130 on the Stanford-Binet 5. Same person, same ability — different number, because the scale is different.
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