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FermiForge

Guess almost anything — to within a power of ten — by breaking it into small pieces.

🔮 Open the estimation console →

What a Fermi estimate is

Nobody can just know how many jelly beans fill a jar. But you can break the question into pieces you can guess — beans in one layer, and how many layers — then multiply. Make a low guess and a high guess for each piece, and the answer gets pinned to about a power of ten: a hundred, a thousand, a million. That is a Fermi estimate, named for a physicist famous for it. The exact number barely matters — knowing which power of ten is a superpower.

  1. Chunk. Break the big question into two or three small ones you can actually guess.
  2. Bound. Give each piece a low guess and a high guess — you don’t need to be exact.
  3. Predict. Which order of magnitude will the answer be — a hundred? a thousand? a million?
  4. Reveal. Multiply it out and watch your estimate land right next to the real answer.

Everything runs on your device — no calculator, no internet, no accounts.

Meet the crew — the five estimation moves

  • Chunk breaks the impossible question into two or three you can guess. Nothing gets estimated until Chunk has split it up.
  • Bound gives every piece a low guess and a high guess — never one number, always a range.
  • Round keeps the numbers friendly, rounding to one clean figure so the maths stays in your head.
  • Sanity (mentor) asks the honest question at the end: does this answer feel right? Is it in the right ballpark?
  • Unit keeps the labels straight — beans per layer, layers, breaths per minute — so nothing multiplies wrong.

Painted friends + storybooks are coming soon.