What does an IQ of 91 mean?
Below the average on the reference scale, at approximately percentile 27.43.
- IQ score
- 91
- Percentile
- 27.43
- At or above
- 72.57%
Normal reference · mean 100 · SD 15. These are calculated values, not observed starp population ranks.
Where 91 sits on the IQ scale
A score of 91 is 9 points below the mean. Dividing by the standard deviation gives (91 − 100) ÷ 15 = -0.6. The normal cumulative distribution converts that standardized position into percentile 27.43.
This lies in the lower half of the central 85–115 interval. A position below the mean is a comparison with the scale center, not a statement that every reasoning skill is below average.
How common is a score of 91?
Approximately 27.43% of this model lies at or below 91—about 1 in 4. This is a cumulative share, not the chance of scoring exactly 91. A continuous model does not assign a positive probability to one exact value.
Compared with IQ 85, the reference percentile is 11.56 percentage points higher. Equal IQ-point gaps do not create equal percentile gaps: the middle of the bell curve contains more area than its ends.
Compare nearby scores
Compare 86 and 91 or calculate 91 on another scale. A small difference between test results is not automatically a meaningful change.
How this relates to starp
starp's current scoring map does not produce exactly 91. Its neighboring results are 90 for 20 correct answers and 95 for 21 correct answers out of 30. This guide explains the conventional scale value 91; it does not invent an intermediate starp result.
See the scoring method and how raw scores differ from IQ estimates.
Questions about IQ 91
Is 91 a good IQ score?
91 is below the reference mean of 100. It should be interpreted in the context of the test, rather than as a verdict on a person's abilities or future.
What percentile is an IQ of 91?
On a normal scale with mean 100 and standard deviation 15, 91 corresponds to approximately percentile 27.43. Around 72.57% of that model lies at or above it. Use an assessment's own norms for an actual reported rank.
Does an IQ of 91 mean 91% correct?
No. IQ is a scaled score. Percentage correct depends on the questions and scoring rules; percentile describes a relative position. These three quantities are not interchangeable.
Method: NIST's normal-distribution formula. Percentiles here are calculated reference values, not observed starp population ranks. About starp scoring.