IQ Scale & Ranges Explained (With Chart)

What is the IQ scale?

The IQ scale is a way of turning test performance into a rank against people your age. It is centered on 100 (the average) and spread with a standard deviation of 15 points, so every 15 points above or below 100 is one standard step away from the middle.

That design comes from the normal distribution, the bell curve. Most people cluster near the middle, and the further you go from 100 in either direction, the rarer the scores get. A score of 115 and a score of 85 are equally common, just on opposite sides.

Two details matter before you read any chart:

• The scale is the same at every age. Scores are age-normed, so 100 is average for 8-year-olds and for 80-year-olds alike. See what the average IQ is for why.
• Most modern clinical tests use SD 15. The Wechsler scales (WAIS for adults, WISC for children) and the Stanford-Binet fifth edition all use a mean of 100 and SD of 15. Some other tests use a different spread (the Cattell scales report with SD 24), so “IQ 148” on one scale can mean the same rarity as “IQ 130” on another.

IQ ranges chart (Wechsler classification)

Here is the standard set of ranges with the descriptive labels used by current Wechsler tests (the WISC-V and WAIS-5 style labels), the older WAIS-IV labels you may still see in reports, and the approximate share of people in each band.

The shares come straight from the normal distribution with a mean of 100 and SD of 15, so they are properties of the scale, not survey results. Real samples match them closely in the middle and less precisely at the extremes.

A few notes on the labels:

• Labels are descriptions, not diagnoses. “Extremely low” does not by itself mean intellectual disability. A diagnosis also requires limits in everyday adaptive functioning that started in childhood, assessed by a professional.
• “Genius” is not a band. No modern clinical test uses it. It’s an informal word, and the old ratio-IQ era attached it loosely to very high scores.
• Other tests use other words. The Stanford-Binet and other batteries have their own descriptors. The numbers line up; the vocabulary doesn’t.

How much of the population falls in each range?

Because IQ follows a bell curve by design, the share of people within a given distance of 100 is fixed:

Read the other way, about 2.3% of people score above 130 and about 2.3% below 70. Above 145, it’s roughly 1 person in 750.

IQ percentiles: 70, 85, 100, 115, 130 and 145

A percentile tells you the share of people your age who score at or below you. This is often more intuitive than the number itself.

Two things stand out. First, the middle of the scale is crowded: going from 100 to 115 moves you past about a third of the population. Second, the top is sparse: going from 130 to 145 moves you past only about 2%.

That has a practical consequence for accuracy. Tests are normed on a few thousand people, so they have plenty of data near 100 and very little above 145. That’s why scores at the extremes are less precise, and why clinical tests have ceilings.

What about the “IQ test range” on a real test?

The range a test can report is narrower than the theoretical bell curve. On the adult Wechsler scale, full-scale scores run from roughly the 40s to around 160. Children’s tests have their own floors and ceilings. Beyond those limits, the test can only say “at least” or “at most.”

Scores above about 160 you see online usually come from one of three places:

1. Old ratio IQ. Before deviation scores, IQ was mental age divided by age, times 100. A child who performed far ahead of their age could get a very high ratio, and those numbers are not comparable to modern scores.
2. Wider scales. A score on an SD 24 scale looks bigger for the same rarity. Converted to SD 15, it shrinks.
3. Estimates. Many famous “IQs” were never measured at all. Einstein’s IQ is the best-known example.

IQ scale vs. what a single score means

The scale tells you what a number would mean if it were measured perfectly. Real scores are not. Every test has measurement error, typically a few points for a full-scale clinical score, so psychologists report a confidence interval (for example, “112, 95% confidence interval roughly 107 to 117”) rather than a single point.

So a score of 109 and a score of 111 straddle the line between “average” and “high average” on the chart, but they are not meaningfully different results. If you want to know how to read your own number, with confidence intervals, retest effects and the difference between online and clinical tests, see what your IQ test score actually means.

How to read the chart without fooling yourself

The chart is clean. The way people use it often isn’t. A few habits help:

• Think in bands, not points. A 104 and a 96 are both plain average. Treat any score as a range of about plus or minus 5.
• Check the scale. Before comparing two numbers, confirm both are on a mean 100, SD 15 scale.
• Check the source. A clinical test given one-to-one by a psychologist and an unnormed online quiz can both print “IQ 128.” Only one of those numbers was calibrated against a representative sample.
• Remember what’s measured. The scale ranks performance on reasoning, verbal, memory and speed tasks. It doesn’t rank judgment, creativity, or how well you make decisions under real uncertainty.

If you want a feel for the kinds of items IQ tests use, the free Mentarium IQ practice test has 30 questions across number series, analogies and logic. It’s practice, not a clinical measurement, and it won’t place you on this chart with clinical accuracy.

The Mentarium take

The IQ scale is one of the cleanest examples of a number that’s easy to misread. It’s a percentile wearing a costume: 130 just means “about the top 2% of a reference sample, on this kind of test, give or take a few points.” Once you translate scores into percentiles and ranges, most IQ arguments online dissolve.

That translation is a general skill. Probabilistic thinking means asking for the distribution behind a number, and good critical thinking means asking how a number was produced before you trust it. Apply both to IQ and you’ll stop treating a 3-point difference as a personality trait.