IQ Distribution Percentiles: Score Conversion Chart
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What Are IQ Distribution Percentiles?
IQ distribution percentiles show where a score falls compared with a norm group. On the common IQ scale, the mean is 100 and the standard deviation is 15. A percentile rank tells you the percentage of the norm group scoring at or below that score.
For example, IQ 100 is the 50th percentile, IQ 115 is about the 84th percentile, IQ 130 is about the 97.72nd percentile, and IQ 145 is about the 99.87th percentile on a normal SD-15 scale.
Quick answer
IQ percentiles convert a standard score into a rank: IQ 130 is about the 97.72nd percentile; IQ 145 is about the 99.87th.
IQ Distribution Percentile Chart
| IQ (SD 15) | Approx. percentile | Approx. share at or above |
|---|---|---|
| 70 | 2.28th | 97.72% |
| 85 | 15.87th | 84.13% |
| 100 | 50th | 50% |
| 115 | 84.13th | 15.87% |
| 120 | 90.88th | 9.12% |
| 125 | 95.25th | 4.75% |
| 130 | 97.72nd | 2.28% |
| 132 | 98.35th | 1.65% |
| 138 | 99.44th | 0.56% |
| 140 | 99.62nd | 0.38% |
| 145 | 99.87th | 0.13% |
How the IQ Distribution Works
The normal-curve model assumes most people cluster near the average and fewer people appear as scores move farther from 100. One standard deviation above the mean is IQ 115, two standard deviations above the mean is IQ 130, and three standard deviations above the mean is IQ 145.
This is why high-end percentile differences look small but can represent large rarity changes. Moving from the 97.72nd percentile at IQ 130 to the 99.87th percentile at IQ 145 changes the top-share estimate from about 1 in 44 to about 1 in 741.
Cautions When Using IQ Percentile Charts
- These conversions assume a mean of 100 and SD of 15.
- Some tests use SD 16 or empirical norm tables.
- Percentile rank is not the same as percentage correct.
- Extreme scores require enough test ceiling to be precise.
- Observed scores should be interpreted with confidence intervals.
Frequently Asked Questions
FAQ
What percentile is average IQ?
IQ 100 is the 50th percentile on a mean-100 scale.
What IQ is the 85th percentile?
The 85th percentile is about IQ 116 on an SD-15 scale.
What IQ is the 98th percentile?
The 98th percentile is around IQ 131 to 132 on an SD-15 scale.
Summary
IQ distribution percentiles translate standard scores into rank within a norm group. On the common SD-15 scale, 100 is average, 115 is about the 84th percentile, 130 is about the 97.72nd, and 145 is about the 99.87th. Use these as approximations unless the test report provides its own norm table.