Fermi - Daily Estimation Game and Survival Mode

How many rivets hold the Eiffel Tower together? How many litres of water pour over Niagara Falls every second? Nobody knows these numbers offhand, but you can get surprisingly close by breaking them into pieces you can picture. That is a Fermi estimate, named after the physicist Enrico Fermi, who was famous for quick, rough and remarkably accurate answers.

This game has two modes. Daily gives everyone the same three questions. Survival keeps the questions coming until one guess lands too far off.

How to play Fermi

1. Read the question and its unit. Every answer is a real number taken from a published source.
2. Break the problem into smaller quantities you can estimate: how many people, how often, how big, how much each.
3. Type your estimate and press Lock it in. You get one guess per question.
4. See the real answer, how many times off you were, and a worked “napkin math” estimate showing one way to get there.

You can type numbers the way you would write them: 1,245, 12k, 3.5 million, 2bn or 4e9. You can also type the calculation itself, such as 8e9 × 0.3 ÷ 4, and the game works it out as you type. The Calculator button opens number and operator keys, which is handy on a phone.

Questions

How is the daily game scored?

Each guess is scored by how many times off it is, too high or too low. A perfect answer is 1×. Guessing half or double the real number is 2×, and a tenth or ten times is 10×. Your score for the day is the geometric mean of your three results, so lower is better and one wild miss does not ruin the whole day.

How does Survival work?

Survival deals one question after another. Land within 10× of the answer, too high or too low, and you carry on. A guess of 50 or 5,000 survives an answer of 500; 40 or 6,000 ends the run. Your score is how many questions you survived in a row, and your best run stays in this browser. A run can be shared, so a friend can face the same questions in the same order.

What do the coloured squares mean?

🎯 is a bullseye, within 1.1× of the answer. 🟩 is close, within 2×. 🟨 is within 5×, and 🟧 is within 10×, which still survives. 🟥 is more than 10× off.

When do new daily questions arrive?

Every day at 00:00 UTC. Everyone gets the same three questions. The calendar button lists earlier days so you can catch up; replays don’t count towards your streak.

Will Survival spoil the daily questions?

No. Survival draws on its own set of questions, plus daily questions only after their day has passed.

Where do the answers come from?

Every answer names its source: statistics offices, scientific papers, official records and organisations such as NASA, the USGS and the UN. Some answers are straightforward calculations, and the answer screen says what they assume. The napkin math shows one reasonable way to estimate the answer, not the only one.

What does sharing show?

Your daily score, one square and factor per question, and whether each guess was too high or too low. The questions and answers are never included, so you can post it without spoiling anyone’s game.

About this edition

This Playdle edition is inspired by the daily game at fermi.gg and by survival-style estimation games. Its questions, worked estimates, scoring details, design and code are its own. There are no accounts or ads, and the game makes no network requests after the page loads.