THE RULES & THE REASONING

How to play Fermigg

Fermigg is a Fermi estimation game: turn an unfamiliar question into a few quantities you can reason about, submit one number, then compare your thinking with the reference answer.

Your first three rounds

1. Choose solo play on the homepage, or select a collection in the question archive.
2. Read the question and its unit. Enter a positive number; the calculator supports arithmetic, parentheses, percentages and π, and scratch notes let you keep your assumptions together.
3. Submit once you are ready. The estimate locks, and the reveal shows your answer, the reference value, your multiplier and a worked explanation.
4. Continue through all three questions. Your final result combines the three multipliers. Review individual rounds before starting another set.

How the multiplier works

Divide the larger of your estimate and the reference answer by the smaller. The result is always at least 1×, and closer to 1× is better. This treats proportional overestimates and underestimates equally.

For a complete solo set, add the three unrounded multipliers and divide by three. Scores of 1×, 1.5× and 2× average to 1.5×. The final calculation uses full precision even when the screen rounds a number for readability.

Reason through an unfamiliar quantity

Suppose you want to estimate the number of seats in a small theatre. Split it into rows and seats per row. If you picture 18 rows with 14 seats each, the estimate is 252. Then check the assumption that matters most: does every row really have the same width, or do aisles and shorter front rows reduce the total?

A useful estimate includes its unit. Rows multiplied by seats per row gives seats; multiplying that answer by the number of performances would instead give seats offered across several shows. Both calculations can be sensible, but only one answers a question about the building's capacity.

Playing with a friend

Choose a friend match on the homepage, enter a name and create a room. Send the invitation link to one other player. You can use different devices and different networks. Both players mark themselves ready, then the host starts the match.

You receive the same three questions. Each round ends when both players submit or the timer expires. Guesses remain hidden from the other player until the reveal. Fewer missed answers wins first; if misses are equal, the lower total multiplier across answered rounds wins. An unanswered round is a miss, not an invented numeric score.

The game runs on cloud servers. Neither player's computer hosts the service, and the server keeps the round timer even if both players disconnect. A temporary reconnect can restore your room while it remains available. After a match, both players can agree to a rematch.

Daily rotation, practice and saved results

There are twelve questions in four collections. The featured collection rotates at midnight in Eastern Time; this is a rotation through the existing library rather than a promise of new questions every day.

Your first completed solo score for each collection is saved in this browser. Replays do not replace it, and scores do not automatically sync to another device. Clearing browser storage can remove your history. Personal scores are available from Your stats and are not public profile pages.

Choose a starting point

Everyday, multiplied provides explicit assumptions for practising conversions. A sense of scale focuses on volume and length. When you want more uncertain inputs, try The big and the small.