How IQ Tests Work and How Accurate They Are
An IQ test scores how well you reason with patterns, words, numbers and shapes, then compares you with other people. Here is how that works, and exactly how our free IQ test turns 25 answers into an estimate.
What does an IQ test measure?
An IQ test measures a mix of reasoning skills that tend to go together. Psychologists group them in a few broad areas: reasoning with new problems, verbal reasoning, spatial thinking, working memory and speed of processing.
The scores on those areas are positively linked. People who do well on one kind of puzzle tend to do well on the others. IQ is a summary of that overlap. It is useful for some questions, such as how someone may cope with certain school tasks. It is not a measure of worth.
How is an IQ score calculated?
On a clinical test, your raw score is the number of points you earn. The test maker has given the test to a large, carefully chosen sample of people. Your raw score is placed on that sample's curve, and then converted to a scale with an average of 100 and a standard deviation of 15.
The key step is the sample. Without a large sample, the numbers on the scale have no firm meaning. A score of 115 means "higher than about 84 in 100 people in the sample", and only if the sample is a good stand-in for people like you.
What is in this test?
The test has 25 questions in four types. Each type tests a different part of reasoning.
- Number series (8). Spot the rule in a list of numbers. This tests pattern finding with numbers.
- Words and logic (6). Analogies, an odd one out and a logic statement. This tests verbal reasoning and careful thinking.
- Matrix puzzles (6). A 3 by 3 grid of shapes follows a rule, and one piece is missing. This is the classic kind of puzzle used to test reasoning with new material.
- Shape rotation (5). Find the same shape, turned. The wrong options are mirror images. This tests spatial thinking.
The matrix and rotation puzzles are drawn by code from the rule behind them, which is how we check that each one has exactly one right answer.
How we calculate your estimated IQ
Each question is worth 1, 2 or 3 points by difficulty. The full test is worth 50 points. We then do three things.
- Add up the points for the questions you got right.
- Take off what a person would score by guessing. On our mix of question formats that is about 23 percent of the points, or 11.5 out of 50.
- Spread what is left over a scale from 70 to 145. Someone at the guessing level gets 70 and someone with all 50 points gets 145. In between, the scale rises in a straight line.
In short: estimated IQ = 70 + 75 x (share of points beyond guessing). We round to a whole number and show a range of 10 points either way.
This is a fixed table that we wrote. It is not built from a norm group, and we have no data on how many people at each age get each score. That is the main reason our result is an estimate and not an IQ score. It also means the same raw result would map to a different number on another site.
How accurate is it?
It is good enough for fun and for a rough sense of how you handle reasoning puzzles. It is not good enough for any decision. The questions are real reasoning tasks, but the test is short, the scale is untested and we cannot control your setting. Our guide to online IQ test accuracy goes through the limits one by one.
Your privacy
All scoring happens in your browser. Your answers are not sent to us. We count anonymous totals, like how many people finish and which range they land in. Details are on the privacy page.
Ready to try it?
Take the free IQ test and then check your result on the IQ score chart.
Curious where you land? The test has 25 questions and the result is free.
Take the free IQ test