Fermi
Rate itThree Fermi questions a day: napkin math, one guess each.
on fermi.gg
Fermi is a daily estimation game. Each day brings three hard-to-know numbers, like the number of iPhones ever made or paper bus tickets printed in London each year; you make one guess per question and are scored on how far off you were as a multiple of the answer.
About Fermi
Fermi takes its name from the physicist Enrico Fermi and the style of question he made famous: rough estimates of hard-to-know quantities built from quick reasoning. Fermi is made by Flatwhite Studios, the small studio behind Spotle and Harmonies, and its first numbered puzzle went up on 27 July 2026. The site gives you three such questions every day, numbered and dated, the same for every player.
You get one guess per question. A built-in calculator is there for napkin math; looking things up is against the spirit of the game. After each guess the real answer is revealed together with an example of how you could have reasoned your way to it, and you see where your guess fell among everyone else's.
Scoring is by ratio: hit the answer exactly and you score 1x, be off by double and you score 2x, off by ten times and you score 10x, so lower is better. Your day's score is the average of the three, shown against other players and ready to share. Players who sign in can join a leaderboard for the day, the week, all time and streaks, and earn badges. A new set arrives at midnight Eastern time, older days are in the archive, and players can submit their own questions.
It suits anyone who enjoys back-of-the-envelope reasoning, from students to consultants practising case interviews.
How to play Fermi
- Open fermi.gg and press Play Today's.
- Read the first question and work out an estimate; tap the calculator icon if you need it.
- Type one guess and lock it in, then see the answer, an example method and how others guessed.
- Answer all three and share your average score: lower is better.
Screenshots
Tips
- Break the question into parts you can estimate, then multiply.
- Being off by a factor counts, not the raw difference, so get the order of magnitude right first.
- Read the example math after each answer: it improves your method.
Questions
How is it scored?
By how far off you are as a multiple of the real answer: 1x is perfect, 2x means off by double. Lower is better.
When does the new puzzle drop?
Every day at midnight Eastern time.
Can I play old puzzles?
Yes, the archive is in the side menu.
Do I need an account?
No. The daily plays without one; signing in is only needed to appear on the leaderboard.
Ratings and reviews
No ratings yet. Be the first to rate Fermi.
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