Market sizing

Estimating market size, ideally bottom-up from real units and prices rather than top-down from an industry report.

Example

12,000 target firms × $4,800/yr = a $58M SAM.

Bottom-up is credible because every assumption is visible and arguable. Top-down ('1% of a $50B market') is the classic amateur slide.

TAM (Total Addressable Market) — The total annual revenue available if you had 100% of a market with no competition.
SAM (Serviceable Addressable Market) — The portion of TAM you could actually serve given your product, geography and business model.
SOM (Serviceable Obtainable Market) — What you can realistically win in the next few years with your actual resources.

What investors are actually assessing — Team, market, traction, insight, and whether the outcome can be large enough. In roughly that order, and mostly in the first ten minutes. (10 min)
The pitch deck — Ten to twelve slides whose only job is to get the next meeting. Not to close the round. (12 min)
Where startup ideas actually come from — Not from brainstorming. From personal pain, professional experience, and things that just changed. (10 min)
Evaluating an idea honestly — Nine dimensions, assessed as evidence rather than as a score. What you know, what you assume, and what is still unvalidated. (15 min)
Market size — TAM, SAM and SOM — How to size a market bottom-up so the number means something, instead of the '1% of a $50B market' slide everyone has seen. (12 min)