Case type 01
Guesstimates and market sizing
How to estimate any quantity from almost nothing: clarify what is asked, build a short formula top-down or bottom-up, segment where it matters, choose assumptions that fit the region, and sanity-check against a real anchor.
32 min2 lessons Last reviewed
Start lesson 1 Cracking any estimation prompt
How do you approach a guesstimate or market-sizing case?
- Clarify exactly what is being counted, for which region and time period.
- Choose top-down or bottom-up, split the population into sensible segments, state each assumption out loud, and sanity-check the result against something you know.
- The most common mistake: jumping to a number without a structure, or using one average for groups that behave very differently.
- Every guesstimate follows five steps: clarify what is being estimated, turn it into a short formula, fill each part with a defensible assumption, calculate, then sanity-check against something you know and say what the number means.
- Estimation gets fast only with practice.
By the end you will be able to
- Clarify what is being estimated before building anything
- Choose between top-down and bottom-up, and check one against the other
- Pick assumptions that fit the region and defend them out loud
- Sanity-check against an outside anchor and stay calm when challenged
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Common questions: Guesstimates and market sizing
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