Estimation test
How long is the Danube? How tall is the Eiffel Tower? In this estimation test you do not have to know the answer. You give a range you are 90% sure contains it, and you find out how often your ranges are right.
Why a range instead of a guess
A single number is almost always wrong by a little, so it says nothing about how much you trust it. A range says both things at once: your best idea of the answer, and how sure you are of it. A narrow range is a strong claim. A wide range is a modest one. Neither is better on its own. What matters is whether your ranges match your knowledge.
How the scoring works
Each question asks for a low and a high number. If the true value falls inside your range, ends included, that range is a hit. A range you are honestly 90% sure of should be a hit about 9 times in 10, so on a typical day of five questions a well-calibrated player gets four or five. If you often catch only two or three, your ranges are too narrow for what you know.
After each answer you see the true value and a link to its source on Wikidata, so you can check it yourself.
How to make a good 90% range
Start from something you do know. If the question is the length of a river, think of a river you know the length of and ask whether this one is longer or shorter. Then set each end of your range at the point where you would be genuinely surprised to be wrong: one chance in twenty below the low end, and one in twenty above the high end.
A common mistake is to anchor on your best guess and add a little on each side. Most people do this, and it is the main reason their ranges miss. If you are unsure, widen the range more than feels comfortable, then see how it scores.
Daily game or full assessment
The daily game takes about a minute: five range questions, the same for everyone each day, with your streak and hit rate kept on your device. The full assessment takes five minutes and adds two-choice questions with a confidence rating, so you also get a calibration chart.
Play the daily estimation game ยท Take the full assessment
Free, with no account and no tracking. Answers are anonymous and go into a public research dataset.