6 min read · Updated 2026-06-01
What is an IQ test? A plain-English guide
IQ tests measure reasoning ability across a few core domains. Here's what they actually measure, what they don't, and how the score is calculated.
An IQ test is a standardised way of comparing one person's reasoning ability to a large reference group. It doesn't measure knowledge, personality, creativity, or motivation. It measures how well you handle a specific kind of thinking task under a specific set of rules.
What IQ tests actually measure
Modern IQ tests break reasoning into four broad domains: verbal (understanding language and analogies), numerical (working with numbers and proportions), spatial (rotating and folding shapes in your head), and logical (drawing conclusions from rules).
Each question is designed so that most people find it possible but not trivial. The score you get back is not a raw count of right answers — it's how your count compares to everyone else who has taken the same test.
The 100-point scale
IQ scores are anchored to a mean of 100 and a standard deviation of 15. That means:
- About 68% of people score between 85 and 115.
- About 95% score between 70 and 130.
- A score of 130 puts you in roughly the top 2%.
- A score of 70 puts you in roughly the bottom 2%.
What IQ tests don't measure
IQ tests don't measure whether you're kind, curious, hard-working, wise, or good at your job. They correlate modestly with academic and professional outcomes, but the correlation is nowhere near 1. Two people with the same IQ can lead very different lives.
Should you take one?
For personal interest, sure. Treat the result as a rough estimate — not a verdict. Any single test has measurement error of roughly ±5 points, and your score will drift a bit with sleep, focus, and practice.
Frequently asked questions
- Is an IQ test the same as an intelligence test?
- In practice, yes — the terms are used interchangeably. Both measure reasoning ability against a reference population using a mean-100, SD-15 scale.
- How long does an IQ test take?
- Short online tests take 10–20 minutes. Full clinical IQ tests (like the WAIS-IV) take 60–90 minutes and require a trained administrator.
- Can you improve your IQ score?
- You can improve your score on a specific test by practising that test's format — but that's called the practice effect, not real gains in reasoning ability. Underlying ability changes slowly.