How the IQ scale works
An IQ score tells you where you rank among people of your age, expressed on a fixed scale. Test publishers convert raw scores so that the norm sample has a mean of 100 and a standard deviation (SD) of 15. Because scores follow a bell curve, the same few percentages apply to every modern test:
- 68% of people score within one SD of the mean, 85 to 115.
- 95% score within two SDs, 70 to 130.
- 99.7% score within three SDs, 55 to 145.
A few tests use a different spread. Older editions of the Stanford-Binet used an SD of 16, and the Cattell Culture Fair scale uses 24, which is why the same person can be "132" on one scale and "148" on another. Always check the SD before comparing numbers.
IQ ranges and their classifications
The labels below are the ones used on Wechsler tests for many years and still the most quoted. The newest editions of the WAIS and WISC replaced "superior" and "borderline" with plainer terms ("very high", "very low"), but the cut-off points did not change.
The shares in the table come from a normal distribution with a mean of 100 and an SD of 15, with each band running from its lower limit up to the start of the next band (so 120 to 129 means 120 up to 130): below 70, 2.3%; 70 to 79, 6.8%; 80 to 89, 16.1%; 90 to 109, 49.5%; 110 to 119, 16.1%; 120 to 129, 6.8%; 130 and above, 2.3%. A single score has a margin of error of a few points on a full clinical test, and more on a short one, so reading your result as a band is more honest than reading it as an exact number. Individual pages such as IQ 115 or IQ 130 explain each score in more detail.
| Band | IQ range | Share of adults |
|---|---|---|
| Very superior | 130 and above | 2.3% |
| Superior | 120–129 | 6.8% |
| High average | 110–119 | 16.1% |
| Average | 90–109 | 49.5% |
| Low average | 80–89 | 16.1% |
| Borderline | 70–79 | 6.8% |
| Extremely low | Below 70 | 2.3% |
IQ percentiles: from score to rank
A percentile says what share of people of your age scored lower than you. Because the scale is fixed, every IQ has the same percentile on every test with SD 15:
- IQ 70: 2nd percentile
- IQ 85: 16th percentile
- IQ 100: 50th percentile
- IQ 110: 75th percentile
- IQ 115: 84th percentile
- IQ 120: 91st percentile
- IQ 125: 95th percentile
- IQ 130: 98th percentile (about 1 in 44)
- IQ 140: 99.6th percentile (about 1 in 260)
- IQ 145: 99.9th percentile (about 1 in 740)
Rarity rises steeply at the top. A 130 is uncommon but not extraordinary: a city of 100,000 adults has around 2,300 people at or above it.
Low IQ: what scores below 85 mean
Scores from 80 to 89 are low average and 70 to 79 borderline. People in these ranges finish school, hold jobs and run households; they may find abstract or fast-paced material harder and benefit from clear, practical instruction.
A score below 70 is one part of the definition of intellectual disability, but never the whole of it. Diagnostic manuals such as DSM-5 require three things: significant limits in intellectual functioning (typically a score around 70 or below, allowing for measurement error), real limits in everyday adaptive skills, and onset during childhood. Severity is now judged by adaptive functioning, not by the IQ number alone. Only a qualified clinician can make that assessment, and an online test cannot. Words such as "stupid" have no place on the scale and no clinical meaning.
A low score on a single test also needs checking before anyone reads much into it. Tiredness, anxiety, poor eyesight, a language the person is not fluent in, or simply misunderstanding the instructions can all pull a result down by 10 points or more. Clinicians therefore look at the pattern across subtests, the person's history and their everyday functioning, and they retest when something does not fit. Online, a very low result most often means the test was rushed or abandoned partway, not that the score reflects ability.
How to find your level on the scale
Start by deciding what you need the result for. For a school placement, a diagnosis, a legal question or a workplace adjustment you need a psychologist and a full battery such as the WAIS-5 or the Stanford-Binet 5; nothing else counts. For curiosity, or to see whether a formal assessment is worth it, a careful online test is enough. A full clinical assessment gives the most precise placement. A well-built online test can place you in a band if it uses enough items, time limits and stated norms. Our IQ test shows your band for free and gives the exact score, percentile and confidence interval in the paid report; our methodology page explains how the norms were built.
Sources
Wechsler, D. WAIS-IV Technical and Interpretive Manual. Pearson, 2008.
American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5). 2013.
Roid, G. H. Stanford-Binet Intelligence Scales, Fifth Edition: Technical Manual. Riverside Publishing, 2003.
Frequently asked questions
What's IQ range?
The IQ range most people fall in is 70 to 130, which covers about 95% of the population. The full reporting range on major clinical tests runs from about 40 to 160; scores outside it cannot be measured reliably.
What is a normal IQ range?
85 to 115, one standard deviation either side of 100, covers about 68% of people. The narrower "average" band, 90 to 109, covers about half.
What is an IQ test range?
It can mean two things. The reporting range of a test is the lowest and highest score it can give, about 40 to 160 for the WAIS and Stanford-Binet. A score range, or confidence interval, is the band your true score probably falls in, for example 108 to 118 for a measured 113.
How can I identify my IQ level?
Take a properly normed test and read the result as a band. A psychologist-administered test is the most precise; a serious online test with time limits and stated norms can give a reasonable estimate of your band.
Is 130 IQ rare?
Fairly. About 2.3% of people score 130 or higher, roughly 1 in 44. It is the threshold many gifted programmes use and close to the 98th percentile that Mensa requires.
What IQ is considered mentally disabled?
A score around 70 or below is one criterion for intellectual disability, but a diagnosis also requires significant limits in everyday adaptive skills that began in childhood. The IQ number alone never decides it.
What IQ is considered stupid?
None. "Stupid" is not a category on any IQ scale. Scores of 80 to 89 are called low average and 70 to 79 borderline; people in both ranges live independent lives, and IQ leaves out many skills that matter day to day.