Your score becomes a rank through the bell curve
Modern IQ tests (Wechsler, WAIS) are built so the population averages 100 with a standard deviation of 15. Convert your score to how many standard deviations it sits from the mean (the z-score), then read the percentile off the normal curve. Every 15 points is one full standard deviation.
IQ, percentile and rarity
| IQ | Percentile | Classification | Rarity |
|---|---|---|---|
| 70 | 2.3% | Borderline | 1 in 44 |
| 85 | 15.9% | Low Average | 1 in 6 |
| 100 | 50.0% | Average | 1 in 2 |
| 115 | 84.1% | High Average | 1 in 6 |
| 130 | 97.7% | Very Superior | 1 in 44 |
| 140 | 99.6% | Exceptionally Gifted | 1 in 250 |
| 160 | 99.997% | Profoundly Gifted | 1 in 31,000 |
The 68-95-99.7 rule is a quick anchor: 68 percent of people score 85 to 115, 95 percent score 70 to 130, and 99.7 percent score 55 to 145.
Two things that change the answer
- The scale's SD matters. Wechsler uses SD 15, Stanford-Binet 16, Cattell 24. The same percentile gives a different raw IQ on each, so an online test using SD 16 is not comparable point-for-point.
- Scores carry error. A real test has a standard error of a few points, so a result of 105 really means a band of about 101 to 109. A single number without that band overstates its precision.
Common questions
What percentile is an IQ of 130?
About the 98th percentile, meaning roughly 2 percent of people score higher. That is the usual cutoff for Mensa. An IQ of 100 sits at the 50th percentile by definition.
Is a percentile the same as a percent score?
No. A percentile is your rank against everyone else, not how many questions you got right. The 84th percentile means 84 percent of people scored at or below you, which corresponds to an IQ of 115.
How rare is a very high IQ?
IQ 130 is about 1 in 44 people, IQ 140 about 1 in 250, and IQ 160 fewer than 1 in 30,000. Above roughly 145 the percentiles are estimates, because standardization samples run out of people that far out.
