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AI Customer Research & ValidationLesson 7 of 13

7 · Sizing your market honestly (TAM, SAM, SOM)

"It's a billion-dollar market!" is the most abused sentence in startup history. Honest market sizing isn't about the biggest number you can justify — it's about a realistic estimate of how many people have your problem and could actually buy from you. The SBA lists the right questions directly: how much demand is there, how big is the market, where are your customers, how saturated is it, and what do competitors charge (SBA, n.d.).

Three honest layers (a standard founder framing):

  • TAM — Total Addressable Market. Everyone who has this problem, in theory. The big, exciting number.
  • SAM — Serviceable Addressable Market. The slice you could actually reach and serve (your geography, your segment, your channel).
  • SOM — Serviceable Obtainable Market. The realistic share you could actually win in the near term, given competitors and your size. This is the number you plan around.

The honest move is to lead with SOM, not TAM. Anyone can claim a giant TAM; a credible founder shows the small, reachable beachhead they can actually win first.

Build it from the ground up, not the sky down. "1% of a billion-dollar market" is a fantasy — it assumes a number instead of earning it. A bottom-up estimate is honest: realistic customers × what each pays × how often. You build it from real, checkable inputs.

Where AI helps — and where it inflates: AI can pull together secondary-research starting points (industry size, demographics, competitor pricing) for you to verify against the SBA's free federal data and other primary sources (SBA, n.d.). But AI will also happily generate a confident, made-up market number if you let it. Treat any figure it gives as a lead to check, never a fact — and never copy a TAM you can't trace to a real source. (Inflating claims to investors or customers also runs into the truthfulness rules in Lesson 9.)

Check yourself. Why is leading with a giant "TAM" weaker than showing a realistic "SOM," and what makes a bottom-up estimate more honest than "1% of a huge market"?

Sources

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