Analysing your IQ
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Convert between IQ scores and percentile rankings in both directions. Supports Wechsler (SD 15) and Stanford-Binet (SD 16) scales.
| Percentile | IQ (SD 15) | IQ (SD 16) | Z-Score | Classification |
|---|---|---|---|---|
| 1st | 65 | 63 | -2.33 | Extremely Low |
| 5th | 75 | 74 | -1.64 | Borderline |
| 10th | 81 | 79 | -1.28 | Low Average |
| 25th | 90 | 89 | -0.67 | Average |
| 50th | 100 | 100 | +0.00 | Average |
| 75th | 110 | 111 | +0.67 | High Average |
| 90th | 119 | 121 | +1.28 | High Average |
| 95th | 125 | 126 | +1.64 | Superior |
| 99th | 135 | 137 | +2.33 | Very Superior |
| 99.9th | 146 | 149 | +3.09 | Genius / Near Genius |
A percentile rank indicates the percentage of scores in a normative sample that fall below a given score. If you are at the 90th percentile, you scored higher than 90% of the comparison group.
IQ scores are derived from the normal distribution. The relationship between percentile and IQ depends on the standard deviation used by the test. The Wechsler scales use SD 15, while the Stanford-Binet uses SD 16. This means the same percentile corresponds to slightly different IQ scores on each scale.
Z-scores express how many standard deviations a value is from the mean. An IQ of 115 (SD 15) has a z-score of +1.0, meaning it is exactly one standard deviation above the average.
An IQ of 130 on the Wechsler scale (SD 15) corresponds to approximately the 97.7th percentile. This means a person with an IQ of 130 scored higher than about 97.7% of the population.
The 90th percentile corresponds to an IQ of approximately 119 on the Wechsler scale (SD 15) or 120 on the Stanford-Binet scale (SD 16).
A z-score indicates how many standard deviations a score is from the mean. An IQ of 115 has a z-score of +1.0 (one standard deviation above the mean of 100). Z-scores make it easy to compare scores across different test scales.
