market-sizing

# Market Sizing A market size is only as good as the assumptions under it. This skill sizes a market two independent ways — **top-down** (start from a published total, narrow down) and **bottom-up** (build up from units × price) — across the **TAM / SAM / SOM** layers, then reconciles them. The goal is a number that survives a skeptical exec or investor, not a single confident-sounding hand-wave. **Grounded in:** *Disciplined Entrepreneurship* — Bill Aulet: bottom-up TAM from a defined beachhead, cross-checked top-down. **Go deeper (The Product Channel):** [The Product Channel](https://sidsaladi.substack.com) The discipline is this: every figure is traceable to a stated assumption, and the two methods are forced to meet. When they diverge wildly, that gap is the finding — it tells you which assumption is doing the heavy lifting. ## When to use this - Filling the market-opportunity section of a PRD, business case, or strategy doc. - Justifying (or killing) a new product, segment, or geo-expansion bet to leadership. - Prepping board, investor, or fundraising materials that need a defensible TAM/SAM/SOM. - Pressure-testing a number a founder, analyst, or vendor handed you that smells inflated. - Comparing two opportunities to decide which is worth the next quarter of build time. ## Before you start (gather these) - **The offering and the buyer** — what exactly is sold, and who pays. "AI note-taking for sales reps" sizes very differently from "meeting software." - **The geog...