TAM, SAM, and SOM explained for first-time founders
One of these numbers is a fantasy, one is a plan, and one is next year. Confusing them is how pitches fall apart.
Three numbers, not one
- TAM — Total Addressable Market: everyone who could theoretically buy this, worldwide.
- SAM — Serviceable Addressable Market: the slice you could actually serve given your product and reach.
- SOM — Serviceable Obtainable Market: the slice you could realistically win in the next year or two.
TAM is the dream, SAM is the strategy, SOM is the forecast. A pitch that quotes only TAM ('it's a $50B market!') tells an investor nothing about whether you can capture any of it.
Estimating without lying to yourself
Build the number bottom-up, not top-down. Instead of '1% of a huge market', start from a real unit: price per customer times the number of customers you can plausibly reach through channels you actually have. The bottom-up number is smaller and far more defensible.
Where it fits in judging an idea
Market size is one of the four dimensions in the MOAT framework, and it's the one founders most often inflate. Tools like Bizwax's MOAT Evaluator will push back on an unrealistic TAM specifically because it's the easiest place to fool yourself — but the fix is the same by hand: size the obtainable market, and be honest about the reach you have today.
Try it on your own keys
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