Guesscale

About Guesscale

Guesscale turns Fermi estimation into a daily game. Every day it serves three questions, such as how far the Earth is from the Sun or how many lightning flashes happen each day, picked from a fixed rotation by date so that everyone gets the same three.

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. Your errors are saved in your browser to build a Scale Profile that shows whether you tend to guess high or low.

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.

How to play Guesscale

1. Open Guesscale to get today's three questions.
2. Break the question into a few quantities you can estimate, using the notes box if you like.
3. Multiply them out and type your final number.
4. Submit to see the reference answer and how many times off you were.
5. Repeat for all three questions, then check your Scale Profile.

Tips

• Aim for the right order of magnitude first; a factor of two is already a good result.
• Write down each assumption so you can see which one was off when the answer appears.
• Watch your Scale Profile: if you keep guessing high, nudge future guesses down.

Questions