A market sizing framework: TAM (Total Addressable), SAM (Serviceable Available), SOM (Serviceable Obtainable Market) — the realistic 3–5 year share you can capture.
TAM SAM SOM is the standard framework for sizing a market in pitch decks. Top-down TAM (industry × wallet share) is fine for pitches; bottom-up TAM (customers × ARPU) is what investors actually trust.
TAM was "all transportation" — they unlocked SAM progressively (taxi → ride-share → food → freight)
SOM was Silicon Valley product teams; TAM expanded to all knowledge workers
A clear TAM SAM SOM tells investors you understand the market. A vague TAM is a red flag.
Bottom-up: Total potential customers × ARPU. Top-down: Industry size × wallet share. Investors trust bottom-up more.
The narrow first segment within your SOM where you win first — small, painful, reachable.
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