Fermi

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. 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. 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

1. Open fermi.gg and press Play Today's.
2. Read the first question and work out an estimate; use the calculator if you like.
3. Lock in one guess, then see the answer, an example method and how others guessed.
4. Answer all three and share your average score: lower is better.

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