Learn about IQ tests and reasoning puzzles

Plain-language guides to what IQ scores mean, how reasoning puzzles work and how to read any online result.

• 1 What does an IQ test measure? Reasoning, the general factor, and the many things an IQ score leaves out.
• 2 The IQ scale explained: what 85, 100, 115 and 130 mean Average 100, SD 15: what each score means as a percentile.
• 3 IQ percentile calculator Turn any IQ score into a percentile, or the other way round.
• 4 Are online IQ tests accurate? Reliability, norms and red flags: how to read any online result.
• 5 Why "free" IQ tests ask for payment at the end The paywall after the last question, how it works and how to avoid it.
• 6 How to solve matrix puzzles The five rules behind 3×3 grids, and a strategy that works.
• 7 Number series: common patterns and how to spot them Steps, ratios, growing gaps and interleaved series, with examples.
• 8 Mental rotation explained Turning shapes in your mind, why mirrors trick you, and how to improve.
• 9 What is the average IQ? 100 by definition, plus age norms, the Flynn effect and online myths.
• 10 Can you improve your IQ score? Practice effects, schooling, sleep and why brain-training disappoints.