Market Size Calculator (TAM, SAM & SOM)
"How big is this, really?" is the first thing an investor wants to know — and a vague answer kills credibility fast. This calculator sizes your market into the three layers investors expect: TAM, SAM and SOM. Build it bottom-up from customers and price, or top-down from a published figure, and get numbers you can defend on a slide.
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Methodology
How it works
TAM, SAM and SOM explained
TAM (Total Addressable Market) is the total annual revenue if every possible customer bought from someone in your category. SAM (Serviceable Available Market) narrows that to the segment your product and geography can actually serve. SOM (Serviceable Obtainable Market) is the realistic slice you can win in the next few years given your team, channels, and competition. Each sits inside the last: TAM ≥ SAM ≥ SOM.
Bottom-up vs top-down
Top-down starts from an analyst's total-market number and applies shares to it — fast, but easy to dismiss as a guess ("1% of a huge market" is the classic red flag). Bottom-up builds the number from first principles: how many customers can you reach, and how much does each pay per year? Investors trust bottom-up far more because every input is something you can defend with research.
The strongest pitch decks show both and reconcile them. Use bottom-up as your primary number and top-down as a sanity check that you're playing in a big-enough pond.
Choosing realistic SAM and SOM shares
Your SAM share should reflect a real constraint — the languages you support, the regulations you meet, the segment your product actually fits. Your SOM share should reflect competition and your go-to-market capacity over three to five years; for most startups that's a low single-digit percentage of SAM, not 10%+. A credible, modest SOM beats an inflated one: it shows you understand the work between today and your revenue ceiling.
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