TAM SAM SOM

TAM SAM SOM is a three-layer way to size a market: the total addressable market (everyone who could ever buy), the serviceable addressable market (the slice your product and geography can actually reach), and the serviceable obtainable market (the share you can realistically win in the next few years). The nesting matters because a billion-pound TAM is meaningless if your SAM is tiny or your SOM is a rounding error. For a lean founder, the honest number is SOM: it tells you whether the niche can fund the next stage or whether you'll hit a ceiling fast. Build it bottom-up from real units (price multiplied by reachable customers), not top-down from an analyst's headline figure. Investors discount top-down sizing on sight, and so should you, because the bottom-up version is the only one that survives contact with your actual pipeline.