Scores & Scales Explained
What a specific number means on a specific scale, why every score needs a confidence range, and how the scales convert.
Stanford-Binet 5 (SB5) Scores Explained: Ranges and Factors
The SB5 reports a Full Scale IQ across five factors for anyone from age 2 to 85 and older, on the same mean-100, standard-deviation-15 scale as the Wechsler tests. See the real score ranges, what one district actually requires for its gifted program, and why a sixth edition already changes what "current" means.
WPPSI-IV Scores Explained: Score Ranges, Composites and IQ
Pearson's WPPSI-IV covers ages 2:6 to 7:7 and reports composites on the familiar 100-and-15 scale. Its sample report shows a Full Scale IQ of 99 built from indexes that run from 63 to 126, and no public table says what score is gifted.
WAIS-IV and WAIS-5 Index Scores Explained: What Each Number Means
A WAIS report is not one number. WAIS-IV gives four index scores and a Full Scale IQ; WAIS-5 gives five indexes, 15 ancillary ones, and an FSIQ built from just seven subtests.
Specific Abilities vs g: What New Reviews Actually Weigh
Does a subtest or index score on an IQ test tell you anything beyond the single full-scale number? Recent reviews reach different answers, largely because they ask the question with different statistical methods.
IQ Z-Scores: How to Turn an IQ Into Standard Units
An IQ z-score counts how many standard deviations a score sits from 100, which is what lets you compare scores from different tests. Here are the formula, a lookup table from IQ 55 to 160, and the point where the table stops being data.
Low IQ and Disability Benefits: What the Score Rules Actually Say
No IQ number qualifies anyone for US disability benefits on its own. Social Security writes 70 and 75 into its intellectual-disorder listing, but each sits inside a three-part test, and a rule many pages still describe was removed in 2017.
Is IQ Linear or Logarithmic? How the Scale Actually Works
Deviation IQ is a straight-line transform of the bell curve — not an exponential or logarithmic one. The confusion comes from somewhere else: the rarity behind each score, which is sharply nonlinear.
What an IQ of 110 Means: Average, High Average, or Both?
On the mean-100, standard-deviation-15 scale most modern tests use, 110 sits at the 74.8th percentile. The WISC-V calls it High Average, the Woodcock-Johnson IV still calls it Average, and the margin of error runs straight across the line between them.
Deviation IQ vs. Ratio IQ: Why the Old Formula Was Replaced
The first IQ scores came from dividing mental age by chronological age. The formula worked reasonably well for children and produced nonsense for adults — which is exactly why every major test replaced it.
The Ceiling on an IQ Test: Why Scores Stop Near 160
A score of 160 is four standard deviations above average — about one person in 31,560. The sample the score is measured against holds roughly 2,200 people, which is why the top of the table is calculated rather than observed.
Full-Scale IQ vs. Index Scores: What's the Real Difference
A Full-Scale IQ is an average of several narrower index scores, and when those indexes disagree by enough, the average describes none of them well.
An IQ Score Is a Range, Not a Number: The Margin of Error
Every properly built test publishes a standard error of measurement alongside the score. On a mean-100, standard-deviation-15 scale it is large enough that a reported 104 and a reported 111 are not reliably different results.
IQ Standard Deviation 15 vs 16: Why One Percentile Has Three Numbers
Wechsler scales use a standard deviation of 15, older Stanford-Binet forms used 16, and the Cattell scales use 24. One standing prints as three different numbers — and one printed 140 is a one-in-260 result on one of those scales and a one-in-21 result on another.
The Mensa IQ Score Requirement Is a Percentile, Not a Number
Mensa admits at the 98th percentile of a supervised, properly normed test. That single rule produces a different qualifying figure on every scale — and none of them is the 130 the internet keeps repeating.
What an IQ of 120 Means, and What It Does Not
On the scale most modern tests use, 120 sits around the 91st percentile. Change the scale and the same number moves. Add the measurement error every test carries and it stops being a point at all.
Written to be checked, not just clicked
Every number carries its scale
An IQ figure is meaningless without the scale it was measured on and the range around it. Every story here reports all three, or says plainly that the source did not.
Sources are listed, not implied
Each story ends with the studies, datasets and documents it draws on, named and attributed, so you can go and read them yourself.
We correct in public
Spotted an error? Write to corrections@iqmetrics.org. Corrections are made on the story and noted at the bottom of it — never quietly.
Read the research.
Then find your own number.
Our IIF-certified assessment reports your score with its scale, percentile and confidence range — and a breakdown of the cognitive domains behind it.
Start IQ Test →