Estimation
Napkin Math
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About Napkin Math
Napkin Math is a free estimation game built on Fermi questions: big, strange questions nobody knows the answer to, but anyone can reason their way close to. Each round has 3 questions, drawn from 60.
Break the question into pieces you do know, multiply it out on the calculator and lock in your guess. You score up to 100 points per question, depending on how close you get. Being within a factor of two is already good.
How to play
- 1Read the question. No Googling. The point is to estimate it.
- 2Break it into smaller numbers you can guess, and use the calculator to work it out. Every sum is noted on your napkin.
- 3Type your answer. You can write 2.5m, 1.2bn or 4,500.
- 4See the real answer and a worked estimate. Score 100 for spot on, less the further off you are.
FAQ
What is a Fermi question?
A question like “how many cups of coffee are drunk worldwide each day?” that you answer with a rough, reasoned estimate instead of looking it up. It's named after physicist Enrico Fermi, who was famous for them.
How is my score calculated?
Each answer scores 0–100 based on how many times off you are. Spot on scores 100, and the score drops as your guess moves away from the true answer, in either direction.
Can I use a calculator?
Yes. There's one built in, and it keeps a handwritten napkin of every sum you do.
Is Napkin Math free?
Yes, free in your browser with no sign-up, and you can play as many rounds as you like.