How to play a Fermi game
- Choose a rough answer before looking anything up.
- Break the quantity into a few factors you can estimate.
- Use the result and the feedback to calibrate your intuition.
What is a Fermi estimation game?
A Fermi estimation game challenges you to estimate quantities that are difficult to know exactly. Instead of recalling trivia, you break a question into smaller assumptions, use rough arithmetic, and aim for the right order of magnitude.
Guesscale turns that method into a daily game: answer three Fermi questions, compare each guess with a reference answer, and learn whether your numerical intuition tends to run high or low.
Why is it called a Fermi game?
Limited information · useful scale
Fermi estimation is named after physicist Enrico Fermi, who became famous for extracting useful answers from limited information and simple assumptions.
During the 1945 Trinity test, Fermi dropped small pieces of paper as the blast wave arrived and used how far they moved to make a rough estimate of the explosion's strength. The same habit of reasoning from imperfect information sits behind every Fermi question.
- 01 Drop paper
- 02 Blast wave arrives
- 03 Estimate from distance
Real question. Rough evidence. Useful estimate. That is the same reasoning loop Guesscale asks you to practice.
Why logarithmic scoring?
Fermi estimates are about scale, not false precision. If the answer is 100, guessing 50 and guessing 200 are both a factor of two away, so Guesscale treats them symmetrically.
Your score is based on multiplicative distance. Your signed error is also saved locally so your Scale Profile can show whether you tend to overestimate or underestimate.
What does the game train?
Repeated estimation builds quantitative intuition: decomposing unfamiliar problems, choosing defensible assumptions, checking orders of magnitude, and calibrating how confident you should be. The goal is not memorizing facts; it is getting better at reasoning about scale.
Example Fermi questions
Good Fermi questions look difficult at first but become approachable once you choose a few reasonable assumptions. Try estimating the answer before opening one of these worked examples:
- How far is Earth from the Sun?Example
- How many people used the Internet in 2025?Example
- How many lightning flashes occur each day?Example
More ways to train
- Practice unlimited Fermi questionsPractice
- Learn the Fermi estimation methodLearn
- Explore Fermi problemsExplore
Fermi game FAQ
What is a Fermi question?
A Fermi question asks for a defensible estimate of a quantity that is difficult to know exactly. The useful skill is decomposing the problem and checking its order of magnitude.
Do I need to know the exact answer?
No. Start with assumptions you can explain, use round numbers, and aim for the right scale. The result includes a reference answer so you can learn after guessing.
Does Guesscale save my guesses?
Your game history and Scale Profile are currently stored in this browser. Cross-device profiles are not available yet.