What Does an IQ of 128 Mean? IQ 128 Percentile, the Gap to Mensa and What One Score Hides
An IQ of 128 is the 96.9th percentile on SD 15, about 1 in 32 people, and 2 points under the usual 130 Mensa line. See what 128 means on SD 16 and SD 24, why no test on American Mensa's list takes it, how far one sitting can move the score, and which famous people sit near it.
An IQ of 128 is the 96.9th percentile on a scale with a mean of 100 and a standard deviation (SD) of 15: about 3 in 100 people score higher. IQ 128 is a high score, and 2 points under the usual 130 Mensa line. On an SD 16 scale it is the 96.0th percentile, and on SD 24 the 87.8th.
New here: no test on American Mensa’s qualifying list takes 128, and the same standing reads 129.9 on SD 16 and 144.8 on SD 24. Below: the percentile, what 128 means on each scale, the gap to Mensa, how far one sitting can move it, and which famous people our pages put near 128.
Key takeaways
- IQ 128 is the 96.9th percentile on SD 15, the 96.0th on SD 16 and the 87.8th on SD 24. On the usual scale that is about 1 in 32.
- American Mensa’s list has no 128 line. The lowest IQ line is 130, and the exact top-2% cut-off on SD 15 is 130.8.
- One sitting gives a range. With a margin of 5 points either side, a 128 could sit anywhere from 123 to 133, which is the 93.7th to the 98.6th percentile.
- No profile on our celebrity pages gives a published IQ of 128. Some estimated ranges start at 128.
What does an IQ of 128 mean?
An IQ of 128 means you scored 28 points above the average of 100, or 1.87 SDs. On the usual scale that puts you above about 97 of every 100 people in the norm group. That is a high score. It is not a rare one, and by itself it is not a diagnosis, a label or a promise about anything else.
What percentile is IQ 128?
An IQ of 128 is the 96.9th percentile on SD 15. About 3.1% of people score higher, or 1 in 32. The 128 IQ percentile is arithmetic on a normal curve, our own calculation, and it holds only if the test’s norm group is close to normal. Our IQ percentile calculator gives the same result for any score, and the IQ bell curve shows where 128 sits.
Natural frequencies make it concrete. In a room of 100 people from the norm group, about 3 would score above 128. In a lecture hall of 300, about 9 would. In a town of 10,000, about 310 would. Each of those counts is the 3.1% tail, so it carries the same assumptions.
| IQ score | Percentile | Share who score higher | About 1 in |
|---|---|---|---|
| 124 | 94.5% | 5.5% | 1 in 18 |
| 125 | 95.2% | 4.8% | 1 in 21 |
| 126 | 95.8% | 4.2% | 1 in 24 |
| 127 | 96.4% | 3.6% | 1 in 28 |
| 128 | 96.9% | 3.1% | 1 in 32 |
| 129 | 97.3% | 2.7% | 1 in 38 |
| 130 | 97.7% | 2.3% | 1 in 44 |
| 131 | 98.1% | 1.9% | 1 in 52 |
| 132 | 98.4% | 1.6% | 1 in 61 |
Is an IQ of 128 the same on every scale?
No. Scales share a mean of 100 but not an SD: 15 on Wechsler tests, 16 on older Stanford-Binet forms and 24 on Cattell tests. Our report on why one percentile has three numbers explains the history. The scale decides what 128 means.
| Scale | Where 128 sits | Percentile of a 128 | Score at the 96.9th percentile |
|---|---|---|---|
| SD 15 (Wechsler) | 1.87 SDs above average | 96.9th | 128.0 |
| SD 16 (older Stanford-Binet) | 1.75 SDs above | 96.0th | 129.9 |
| SD 24 (Cattell) | 1.17 SDs above | 87.8th | 144.8 |
So check which scale your report uses before you compare. A 128 on SD 24 is a far weaker result than a 128 on SD 15. An online result that does not state its SD is the weakest case.
Is 128 enough for Mensa?
No. Mensa asks for the 98th percentile or higher, and 128 is the 96.9th. American Mensa’s qualifying-scores page, which we read on 12 November 2026, lists no test with a 128 line. Its lowest IQ lines are 130, for example on the Wechsler tests and the Stanford-Binet 5, with 132 on the older Stanford-Binet and 148 on the Cattell.
On SD 15 the exact 98th percentile is 130.8, so 128 is 2.8 points short. On SD 16 the line is 132.9 and on SD 24 it is 149.3. Our guides to the Mensa IQ requirement and to what Mensa counts set out the rules. Our post on an IQ of 132 goes through the lines test by test.
Is an IQ of 128 good?
Yes. A 128 is higher than about 97 in 100 people in its norm group, and it is 28 points over the average. Whether it is good enough depends on the cut-off you face. It is below the 130 line used by Mensa. Is IQ 128 good for everyday life? A test score describes how you did on one set of puzzles, on one day, against one norm group. It does not set a limit on what you can learn or do.
How does an IQ of 128 compare with 125, 131 and 135?
A 128 is 3 points above a 125 (the 95.2nd percentile), 3 below a 131 (the 98.1st) and 7 below a 135 (the 99.0th). Read the pages on 125 and 131 for each neighbour. The steps between them are small. One point near 128 is worth about half a percentile point.
Where would your own score land?
Take the IIF-certified assessment and get your score with the scale it was measured on, the percentile it corresponds to and the confidence range around it — the three figures most online tests leave out.
Find your IQ score now! →How accurate is one 128 score?
Not very. A single score is a range. Our report on the IQ margin of error says a well-normed adult test on SD 15 typically has a standard error of 2 to 3 points. That makes a 95% interval about 5 to 6 points either side. We took the figure from that report, not from a test manual.
Apply it to 128: the range runs from about 123 to 133. That is the 93.7th to the 98.6th percentile. So one 128 cannot tell you whether you are above or below Mensa’s 130 line. A person can score 128 on one test and 121 on another.
Which famous people have a 128 IQ?
None, as a published score. We checked every profile in our celebrity IQ section. No one has a published figure of exactly 128, so there is no list of famous people with 128 IQ to give you.
A few estimated ranges start at 128. Ernest Hemingway is placed at 128 to 145 by an achievement-based estimate, with no test behind it. Derek Muller of Veritasium is placed at 128 to 140, around a reported 134. A range is not a score: it is our estimate of where a result could fall.
What does a 128 on an online test mean?
Treat an online IQ test 128 as a rough guide. Online tests use their own norm groups, often volunteers, and many do not say which SD they use. A 128 IQ test result from a website is not the same as a 128 from a supervised test with a trained examiner. Compare it with the scale it states, then place it with the percentile calculator.
If two online tests give you 128 and 119, that spread is normal: each has its own norm group. Online averages also feed country rankings, and our post on the average IQ in Japan shows how weak those can be.
For a score of your own, take the IQ test. Our page on the IQ score converter moves a score from one scale to another.
Quick answers
- What is an IQ of 128? The 96.9th percentile on SD 15, about 1 in 32 people. On SD 16 it is the 96.0th, and on SD 24 the 87.8th.
- Is 128 IQ good? Yes. It is higher than about 97 in 100 people, and 2 points under the 130 Mensa line.
- Is an IQ of 128 enough for Mensa? No. American Mensa’s list has no 128 line, and the exact 98th percentile is 130.8 on SD 15.
- What does 128 IQ mean on different scales? The same standing is 129.9 on SD 16 and 144.8 on SD 24.
- Who has a 128 IQ? No celebrity profile on our site gives a published 128. Hemingway and Veritasium have estimated ranges that start there.
The bottom line
A 128 is a strong result: the 96.9th percentile on the usual scale. The 128 IQ meaning depends on the scale, on the test, and on a margin of a few points either side. IQ 128 does not clear Mensa’s line, because no test on that list sits at 128. If your result is close to a cut-off, a second sitting on a different test is the fair way to find out more.
Sources
- American Mensa. Test scores accepted for membership (page read 12 November 2026).
- IQ Metrics. An IQ score is a range, not a number: the margin of error (2 September 2026).
- IQ Metrics. IQ standard deviation 15 vs 16: why one percentile has three numbers.
- Percentiles, 1-in-N figures and cut-offs on this page are our arithmetic on a normal curve with mean 100; they are not published test norms.
Keep reading
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Scores & ScalesWhat Does an IQ of 131 Mean?
An IQ of 131 is the 98.1st percentile on SD 15 (about 1 in 52) but the 97.4th on SD 16 (about 1 in 38). Mensa lists 131 as the exact line for two tests and 132 for eight more, so the same score can qualify on one test and miss by a point on the next.
Scores & ScalesWhat an IQ of 125 Means
An IQ of 125 is the 95th percentile on the standard scale: about 1 person in 21, in the Superior band and one band below most gifted cutoffs. See how many people that is, what an IQ between 115 and 125 means, how accurate a single score is and what a 125 predicts.
Scores & ScalesMensa IQ Score Requirements
Mensa admits the top 2% of scorers, but "the top 2%" is a rank, not a number, and the number it maps to changes with the test you sat. Here is what qualifies on the Wechsler, Stanford-Binet and Cattell scales, the two routes to membership, and what the supervised admission test is actually like.