Question
Is an IQ score a percentage?
Updated
Short answer
No. An IQ score is a standard score, not a percentage. An IQ of 120 does not mean 120% or 120 right answers. It means you scored 1.33 standard deviations above the average for your age. The matching percentile, about 91, is a separate number: the share of people expected to score below you.
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Three different numbers
- Raw score: how many items you got right. See raw score.
- IQ: where that raw score falls on a scale where your age group averages 100 and the standard deviation is 15 (Wechsler, 2008).
- Percentile: the share of people expected to score below that IQ. See percentile.
IQ and percentile side by side
| IQ | Percentile |
|---|---|
| IQ 70 | 2.3 |
| IQ 85 | 15.9 |
| IQ 100 | 50 |
| IQ 115 | 84.1 |
| IQ 120 | 90.9 |
| IQ 130 | 97.7 |
The relationship is not a straight line. Near the middle, a few IQ points move the percentile a lot: going from 100 to 115 moves you from the 50th to about the 84.1th percentile. Out in the tails, the same 15 points move it only a little, because few people score there. That is the shape of the bell curve: about 68% of people fall between 85 and 115 (NIST/SEMATECH e-Handbook, normal data).
Try one · Logical Reasoning
Which tile completes the second pair?
Tap the option you think is right, or show the answer.
Show the answer
The missing panel shows a large outlined triangle pointing up on its own (option 4).
How to solve it
- Compare the first two panels and name exactly what changed.
- The whole figure is flipped upside down, top to bottom.
- The large shape becomes outlined.
- Nothing else changes.
- Apply the same changes to the third panel: a large solid triangle pointing down on its own.
- So the missing panel shows a large outlined triangle pointing up on its own.
That was 1 puzzle. The full test has 25.
Why the confusion is so common
School tests are usually marked as a percentage of questions right, so a number like 120 looks like it should be out of 100. An IQ works differently. The scale has no maximum of 100 and no fixed top at all; it only has a middle (100) and a unit of spread (15 points). A score above 100 simply means above the middle. A percentile, by contrast, really is a percentage, just not of questions: it is the percentage of people your age expected to score below you.
Which number is more useful?
For most people the percentile is easier to understand, because it answers the question you probably have: how do I compare? The IQ number is more useful when comparing tests on the same scale. Convert any score with the IQ percentile calculator, or see how IQ is calculated for where the number comes from.
Sources
- NIST/SEMATECH e-Handbook of Statistical Methods, section 6.5.1, "What do we mean by Normal data?" National Institute of Standards and Technology. www.itl.nist.gov/div898/handbook/pmc/section5/pmc51.htm
- Wechsler, D. (2008). WAIS-IV Technical and Interpretive Manual. Pearson.