IQ Percentile
Calculate your IQ percentile using the normal distribution (mean 100, SD 15 or 16). Free IQ percentile finder with z-score, classification, and population comparison charts.
About This Calculator
The IQ Percentile Calculator determines what percentage of the population scores at or below your IQ score. IQ (Intelligence Quotient) follows a normal distribution with a bell curve shape — most people score near the average of 100, and fewer people score at the extreme high or low ends. This calculator uses the cumulative distribution function (CDF) of the normal distribution via the error function (erf) to compute an exact percentile from your IQ score.
To use this calculator, enter your IQ score from a reliable standardized test such as the Wechsler Adult Intelligence Scale (WAIS), Wechsler Intelligence Scale for Children (WISC), or Stanford-Binet Intelligence Scale. Select the standard deviation used by your test — SD=15 for most Wechsler and Woodcock-Johnson tests, or SD=16 for Stanford-Binet tests. The calculator then computes your z-score, percentile rank, and classification (from Extremely Low to Profoundly Gifted).
This tool is intended for educational and informational purposes. It does not replace professional psychological assessment. IQ scores from online tests may not be reliable — only standardized tests administered by licensed professionals should be used for classification.
Regional Notes
Global: IQ tests and norms are standardized within each country. The Wechsler scales are the most widely used internationally, with local norms for the US, UK, India, Canada, Australia, and many other countries. The mean is always set to 100 with SD=15 (or 16 for Stanford-Binet). Percentile interpretation is consistent across all regions since the normal distribution is the universal model.
Frequently Asked Questions
What is an IQ percentile?
An IQ percentile tells you what percentage of the population scores at or below your IQ score. For example, if your IQ is 130 (98th percentile for SD=15), only 2% of people have a higher IQ than you. Percentiles are calculated using the normal distribution with a mean of 100 and standard deviation of 15 or 16 depending on the test.
What IQ is considered gifted or genius?
On the Wechsler scale (SD=15), an IQ of 130 and above (98th percentile) is classified as Very Superior or gifted. For the Stanford-Binet scale (SD=16), 130+ is Superior. The 99th percentile corresponds to IQ 135 (SD=15). Only about 2% of the population scores above 130.
How is IQ percentile calculated?
The IQ percentile is calculated by converting your IQ score to a z-score using the formula z = (IQ - 100) / SD, then finding the cumulative probability of that z-score under the standard normal distribution using the error function (erf). The result is multiplied by 100 to get a percentage.
What is the average IQ score?
The average IQ score is 100 by definition. About 68% of the population scores between 85 and 115 (within one standard deviation), and 95% score between 70 and 130 (within two standard deviations). IQ follows a normal distribution with a bell curve shape.
What is the difference between SD 15 and SD 16 IQ scales?
SD 15 is used by the Wechsler Adult Intelligence Scale (WAIS), Wechsler Intelligence Scale for Children (WISC), and Woodcock-Johnson tests. SD 16 is used by the Stanford-Binet Intelligence Scale. The same raw IQ score corresponds to a different percentile on each scale. Always check which standard deviation your test uses.
What IQ score is in the top 1%?
An IQ score of 135 corresponds to the 99th percentile on the Wechsler scale (SD=15), meaning only 1% of the population scores higher. On the Stanford-Binet scale (SD=16), 135 is slightly above the 98th percentile. A score of 140 is in the 99.6th percentile (SD=15).
Is this IQ percentile calculator accurate?
This calculator uses the standard normal distribution CDF based on the error function (erf) approximation, the same mathematical method used by professional psychometric tools. It is accurate for any IQ score between 40 and 200. However, always consult a licensed psychologist for official IQ assessment and interpretation.
What IQ classification is considered extremely low?
An IQ below 70 (2nd percentile for SD=15) is classified as Extremely Low on the Wechsler scale and corresponds to the Borderline or Mildly Impaired range on other scales. This classification requires professional clinical evaluation and should not be self-diagnosed.