IQ tests are scaled so that the average is 100 and two-thirds of people score between 85 and 115. About 2% score 130 or above, the usual threshold for giftedness, and about 2% below 70.
How to use the IQ Percentile Calculator
- IQ score
- Standard deviation of the test
- Every result field is editable: type into Percentile and IQ score plus every other field update to match.
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the IQ score (most modern tests use SD 15; Stanford–Binet editions before 2003 used 16, Cattell 24).
Tips
- Measure lying length for babies under 2 and standing height from age 2.
- Use the exact age in months for babies – a few weeks matters.
- Follow the trend across several visits; crossing two major percentile lines is more important than one value.
- Discuss concerns with your paediatrician.
Common mistakes to avoid
- Comparing a baby with the wrong sex chart.
- Reading the 50th percentile as “normal” and everything else as abnormal.
- Using corrected age incorrectly for premature babies.
Inputs explained
| Field | What to enter |
|---|---|
| IQ score | A number |
| Standard deviation of the test | A number |
What each result means
- Percentile = ncdf(([IQ score] – 100)÷[Standard deviation of the test])×100
- z-score = ([IQ score] – 100)÷[Standard deviation of the test]
- One in = 1÷(1 – [Percentile]÷100)
Example values
How the main result changes when IQ score changes and everything else stays at the example values above:
| IQ score | Percentile (%) |
|---|---|
| 60 | 0.4 |
| 90 | 25.2 |
| 120 | 90.9 |
| 150 | 100 |
| 180 | 100 |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
z = (IQ − 100) ÷ 15
Percentile = Φ(z) × 100
Rarity: 1 in 1 ÷ (1 − percentile)
Worked example
Inputs — IQ score: 120; Standard deviation of the test: 15.
Results — Percentile = 90.9 %; z-score = 1.33; One in = 11; Wechsler classification = Superior.
Key terms
- z-score
- Number of standard deviations from the mean.
Frequently asked questions
What is an average IQ?
100, with 90–109 classed as average.
What percentile is an IQ of 130?
About the 98th percentile.
Is IQ fixed?
It is fairly stable in adulthood but can change with education and environment.
Sources
- Wechsler D. Wechsler Adult Intelligence Scale – Fourth Edition, technical manual. Pearson, 2008