The IQ Scale: A Complete Classification Chart

How the IQ scale works

An IQ score is a rank expressed as a number. Publishers give a new test to a large sample that mirrors the population, then convert each raw result into a deviation score: 100 for the sample's average and 15 points for each standard deviation. The WAIS-IV, published in 2008, was standardized on 2,200 US adults aged 16 to 90. The WAIS-5, released by Pearson in 2024, collected its norms in 2023 and 2024.

The bell curve then fixes the proportions. About 68 percent of people score between 85 and 115, and about 95 percent between 70 and 130. Only about 2.3 percent score above 130, and the same share below 70.

The first IQs worked differently. William Stern compared a child's mental age with chronological age, and Terman multiplied the ratio by 100. Ratio scores do not work for adults, whose performance stops rising with age, so modern tests replaced them with deviation scores. For the background, see the history of the IQ test, how IQ is measured and the IQ score distribution.

The master chart: IQ ranges and labels

The table aligns the three current classification systems. Share of people is the theoretical proportion on a normal curve with a mean of 100 and a standard deviation of 15.

*Pearson's published WAIS-5 sample reports show the five middle descriptors: a 124 is Very high, a 111 Above average, a 94 Average, an 82 Below average and a 79 Very low. The outer labels, Extremely high and Extremely low, are the terms Pearson uses at those levels on the WISC-V; check them against the WAIS-5 manual before quoting a report.

Wechsler: from Very Superior to Extremely high

David Wechsler published his first adult scale, the Wechsler-Bellevue, in 1939, with labels that now read as blunt: 128 and over Very Superior, 120 to 127 Superior, 111 to 119 Bright Normal, 91 to 110 Average, 80 to 90 Dull Normal, 66 to 79 Borderline, and 65 and below Defective.

The WAIS-IV kept Very Superior and Superior at the top, moved the bands to round numbers and put Extremely Low where the 1939 bottom label had been. Pearson's children's scale, the WISC-V, then switched to neutral terms: Extremely High, Very High, High Average, Average, Low Average, Very Low and Extremely Low. The WAIS-5 goes further in the middle, using Above average and Below average for the bands beside Average.

The direction is consistent: from judgment toward description. A label now says where a score falls on the curve, not what kind of person earned it. See how the bands play out at IQ 120, IQ 125 and IQ 130.

Stanford-Binet 5: the scale that still says gifted

The Stanford-Binet Intelligence Scales, Fifth Edition, by Gale Roid, appeared in 2003. It reports IQ with a mean of 100 and a standard deviation of 15, matching the Wechsler tests; older Stanford-Binet forms used 16. Unlike the Wechsler scales, its top labels name giftedness: 130 to 144 is Gifted or very advanced, and 145 to 160 is Very gifted or highly advanced.

That split matters when comparing score pages. An IQ of 141 is still Gifted or very advanced, while an IQ of 147 or 149 is Very gifted or highly advanced. On the WAIS-IV, all three are simply Very Superior. At the other end, the SB5 is more granular, dividing low scores into borderline, mild and moderate impairment or delay.

Terman's 1916 labels, and why genius vanished

Lewis Terman's 1916 Stanford revision of the Binet-Simon scale produced the first widely used IQ classification in English. Its bands applied to ratio IQs, and its language was of its time.

Terman's own Genetic Studies of Genius used 140 as its entry line. Yet by the 1937 second revision of the Stanford-Binet he no longer used genius as a classification, and no later IQ test has. The terms at the bottom of the scale fell away for a different reason: they became insults. In the United States, Rosa's Law replaced mental retardation with intellectual disability in federal law. For the threshold argument, see IQ 140 and what IQ is genius.

Gifted levels: the Gross scale

Researchers in gifted education often subdivide the top of the curve. A widely used scheme comes from Miraca Gross:

The upper levels outrun modern measurement. The WAIS-IV full-scale range stops at 160, so scores in the two highest bands come from ratio IQs, extended norms or older tests. See IQ 160, IQ 180 and IQ 200 and above for what those numbers can and cannot mean.

Other scales: why 148 can equal 130

Not every test uses a standard deviation of 15. Older Stanford-Binet forms used 16, and Cattell-style scales use 24. The same rank therefore carries different numbers, which is why Mensa lists 130 for Wechsler tests, 132 for the Stanford-Binet and 148 for the Cattell.

Ask which scale a score uses before comparing it. A 148 on a Cattell scale equals a 130 on the Wechsler, while an IQ of 148 on the Wechsler scale is about 1 in 1,455. The Mensa IQ test guide covers the tests Mensa accepts.

How to read the label on a real report

Classification labels describe position. They are not diagnoses and not verdicts on a person, and a clinician reads them alongside index scores, history and the purpose of the assessment.

Band edges are softer than they look. A single score carries a confidence interval of roughly five points either way, so a 129 and a 131 are statistically hard to tell apart, even though the WAIS-IV calls one Superior and the other Very Superior. Pearson's WAIS-5 sample report prints a full-scale 111 with a 95 percent interval of 106 to 116.

To turn any label into rarity, use the IQ rarity chart. For the thresholds people ask about most, see what counts as a high IQ and the top 1 percent IQ. For the gap between a clinical label and an online number, read are online IQ tests accurate.

Editorial standard: IQ figures for historical figures are retrospective estimates and are labeled as such; scores for living people appear only when the person disclosed them or a reputable outlet reported them. Corrections: contact the editors.