TAM, SAM, and SOM are the three layers of a market sizing analysis used in pitch decks to help investors understand the scale of the opportunity being pursued and whether the company has the potential to become a venture-scale business.

TAM (Total Addressable Market) is the total revenue opportunity if the company captured 100% of the market with no constraints — no competition, no geographic limits, no segment restrictions. It defines the theoretical ceiling of the opportunity.

SAM (Serviceable Addressable Market) is the portion of the TAM that the company's current product and go-to-market strategy could realistically serve, given its current offering, geographic focus, and customer segment. A global HR software company whose product only supports English-language compliance has a SAM far smaller than its TAM.

SOM (Serviceable Obtainable Market) is the portion of the SAM the company can realistically capture in the near term — typically over 3–5 years — given competition, sales capacity, and distribution constraints. This is the number that should connect to the company's financial projections.

The most common mistake founders make is presenting only a top-down TAM. "The global logistics market is $400B, and we're going after 1%" is a formula investors have seen thousands of times — and it tells them nothing useful. A 1% share of a $400B market requires knowing: 1% of which segment? At what price? Through which channel? Against which competitors?

Bottom-up market sizing is far more credible. Start with the specific customer type you're targeting, count how many of them exist in your initial market, multiply by the expected annual contract value, and show the math. Then explain how adjacent segments expand the opportunity over time. For example: "There are 12,000 mid-market HR teams in North America with 100–500 employees. At $18K ACV, that's a $216M SAM — and we're targeting 250 customers in year one." This kind of specificity signals real market understanding.

In emerging markets or new categories, top-down TAM sizing is sometimes the only available method. In these cases, the most credible approach is to cite third-party market research, explain the assumptions behind the size estimate, and show the tailwind (regulatory change, technology unlock, or demographic shift) driving expansion.