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IIF Certified Assessment
An IQ score means nothing without the scale it was measured on. Enter yours once and watch it land in the same place on every scale — while the number printed there changes completely.
The same person, on every scale
The dashed line does not move between rails. Only the numbers printed under it do.
| Scale | Used by | Score | 95% range | Percentile |
|---|---|---|---|---|
| SD 15 | Wechsler (WAIS/WISC) · Stanford-Binet 5 | 130 | 121–139 | 97.7% |
| SD 16 | Stanford-Binet L-M / IV (retired) | 132 | 122–142 | 97.7% |
| SD 24 | Cattell III B | 148 | 133–163 | 97.7% |
A score of 130 on SD 15 is the same ability as 130 on SD 15, 132 on SD 16, 148 on SD 24. All three describe the same person: 97.7% of people score lower.
Converting does not add precision. At r = .90 the 95% range is 121–139 on SD 15, and it converts along with the score rather than shrinking.
The maths is exact. The test behind it might not be. This tool moves any number between scales without losing a decimal — including a number that was never properly normed. If yours came from a quiz that never named its standard deviation, converting it just restates the same guess in new units.
An IQ score is not a measurement like centimetres. It is a rank, re-expressed on whatever ruler the test publisher chose. Change the ruler and the number changes, even though nothing about the person did.
Your raw answers are turned into a position in the population — how far above or below the average you sit, measured in standard deviations. That position is the only real quantity.
Wechsler decided one standard deviation would be worth 15 points. Cattell III B decided 24. Neither is more correct. The same position simply gets stamped with a different number.
Because the percentile is the position itself, it is identical on every scale. If you only quote one number from a report, quote that one — it cannot be misread.
Read across a row and every cell is the same person. The percentile column is the anchor: it is what the other three columns are all trying to express.
| Percentile | SD 15 Wechsler · SB5 | SD 16 SB L-M (retired) | SD 24 Cattell III B | Rarity |
|---|---|---|---|---|
| 2.28% | 70 | 68 | 52 | 1 in 44 below |
| 15.87% | 85 | 84 | 76 | 1 in 6 below |
| 50% | 100 | 100 | 100 | the middle |
| 84.13% | 115 | 116 | 124 | 1 in 6 above |
| 90.88% | 120 | 121.3 | 132 | 1 in 11 above |
| 97.73% | 130 | 132 | 148 | 1 in 44 above |
| 99.62% | 140 | 142.7 | 164 | 1 in 261 above |
| 99.87% | 145 | 148 | 172 | 1 in 741 above |
The row that causes the most confusion is the highlighted one. Mensa’s published entry requirement is the 98th percentile, and because that percentile is a different number on every ruler, the qualifying score has to be stated separately for each test — around 130–132 on SD 15 and SD 16 tests, and 148 on Cattell III B. Someone quoting “148” is not claiming a higher ability than someone quoting “130”; they are quoting a different scale. Note also that 130 on SD 15 is strictly the 97.73rd percentile, not the 98th — the 98th is 130.81.
Give this converter a number and a scale and it will place that number on every other scale exactly. What it cannot tell you is whether the number deserved converting. A 148 from a five-minute quiz converts just as neatly as a 148 from a properly normed assessment — and lands on the same tidy percentile. The ruler is only as good as the measurement you took with it.
Scored on the standard scale — mean 100, standard deviation 15 — the scale this converter treats as its reference.
Convert the score to a z-score first — subtract 100 and divide by the standard deviation of the scale it came from — then multiply by the standard deviation of the scale you want and add 100. The converter above does this in both directions. How IQ tests work explains where standard deviations come from. An IQ of 130 on an SD 15 test is z = 2.0, which is 132 on an SD 16 test and 148 on Cattell III B.
Only the size of one standard deviation. SD 15 is used by the Wechsler tests (WAIS and WISC) and by Stanford-Binet 5. SD 16 was used by the older Stanford-Binet L-M and fourth edition, which are retired. The gap between them is small near the average and grows at the extremes: 100 is 100 on both, but 145 on SD 15 is 148 on SD 16. The IQ bell curve shows why the gap widens at the extremes.
Because Cattell III B uses a standard deviation of 24 instead of 15, so every point of ability is worth more points of score. A Cattell 148 and a Wechsler 130 are the same result — both are two standard deviations above the mean, and both are the 97.73rd percentile — see the percentile calculator. Comparing the raw numbers without the scale is the single most common IQ mistake.
No, and the converter shows this deliberately. The 95% confidence range converts along with the score, so it stays exactly as wide in relative terms. A score of 130 with a range of 121–139 becomes 148 with a range of 133–163 — the uncertainty travels with you. Converting changes the units, never the certainty. Our page on how accurate IQ tests are covers where that range comes from.
Quote the percentile. It is the one figure that is identical on every scale and cannot be misread as higher or lower than it is. If you do quote an IQ number, always name the scale beside it — “130 on SD 15” is meaningful, “130” on its own is not. The full toolkit, including the percentile calculator and the bell curve, sits on the IQ Tools page.
Yes. It runs entirely in your browser, is free to use and needs no account. Nothing you type is sent anywhere — our Security and Privacy Policy covers how the rest of the site handles data.
The percentile is the one figure that does not change when you convert, which is exactly why it is the safest thing to quote. IQ 130 on SD 15, 132 on SD 16 and 148 on Cattell III B are all the 97.7th percentile. The IQ percentile calculator gives the exact figure for any score, and the IQ bell curve shows where it falls on the distribution.
Only after putting both on the same scale — otherwise you are comparing rulers, not ability. Convert both to the same standard deviation, or compare percentiles instead. The IQ comparison tool is built for exactly that, and tells you whether the gap between two results is real or inside the margin of error.
No. Scale conversion is pure arithmetic and is independent of age. What age does affect is the norm group your raw performance was compared against in the first place, since scores are always normed within an age band. IQ and age explains how different abilities shift across a lifetime.
Some movement is normal and is not a conversion error. An unusually high or low first result tends to drift back toward your average on a retest — a statistical effect, not a change in ability. Regression to the mean explains why, and IQ over time covers longer-term change.
This tool translates a score you already have. Take the assessment to get one measured properly — with the scale, the percentile and the confidence range stated up front.
