Guesscale

Guesscale turns Fermi estimation into a daily game. Every day it serves three questions, such as how many breaths a resting adult takes in a day, picked by date from a rotation of 40 questions on everyday life, science, geography, technology and business, so everyone gets the same three. The rotation started on 16 September 2026, and with three questions a day a question comes back after about two weeks.

The idea, named after the physicist Enrico Fermi, is to reach a sensible answer by breaking a question into a few rough factors and multiplying them out, instead of recalling a fact. The game gives you a notes box for that working and a number field for your final guess.

Scoring is about scale rather than precision. Being twice too high counts the same as being half as much, and feedback runs from Bullseye scale and Excellent calibration down to Right order of magnitude and Way off scale. Each answer earns up to 1,000 points, shown on a log scale with your guess beside the reference answer. Your errors are saved in your browser to build a Scale Profile that shows whether you tend to guess high or low, and finishing the three keeps a daily streak and gives a result to share on X.

There is also an unlimited practice mode and a set of worked example questions. It suits people who like numbers, science and back-of-the-envelope reasoning.