Market Size Calculator

TAM, SAM, and SOM are three nested views of the same market — each answers a different fundraising or planning question.

• TAM (Total Addressable Market): full revenue if one company served 100% of demand. Frames ambition, not forecasts.
• SAM (Serviceable Addressable Market): the TAM slice reachable with your current product, pricing, language, and geography.
• SOM (Serviceable Obtainable Market): the SAM share you can credibly win in 3-5 years given team, capital, and competition.

Investors read all three together. Reporting only TAM looks generic; reporting all three forces you to be explicit about constraints and assumptions.

Use bottom-up as the primary number, then cross-check with top-down. A repeatable market size calculator workflow:

1. Define the buyer precisely — industry, size, role, geography — so customer count is defensible.
2. Estimate target customers via directories, registries, LinkedIn filters, or industry reports.
3. Multiply by realistic ARPU or ACV at current pricing, not aspirational pricing.
4. That product is bottom-up TAM. Apply serviceable % for SAM and year-3 share for SOM.
5. Run top-down separately (industry revenue × segment % × geography %) and compare.

Within ~30% agreement is reasonable; large gaps mean a pricing or share assumption needs resolving.

Both estimate the same market from opposite ends, with different failure modes.

• Bottom-up: starts from buyer count × revenue per customer. Grounded in your product and pricing, so it is more defensible to investors.
• Top-down: starts from published industry revenue, narrowed by segment, geography, and channel. Fast for sanity checks but easy to inflate.

In practice, bottom-up is the number you defend in a meeting; top-down checks whether bottom-up is in the right zip code. If top-down is 10× bottom-up, you are likely under-counting customers or under-pricing. Show both methods in fundraising materials and explain the gap.

Accuracy depends on input quality, not formula complexity. Five practices keep estimates trustworthy:

• Source every assumption — Gartner, Statista, IBISWorld, internal pipeline, or customer interviews.
• Use conservative, baseline, and optimistic scenarios — a single number hides uncertainty.
• Re-check pricing yearly: ACV drift alone moves TAM 20%-30% in a stable market.
• Avoid double-counted segments: a customer fitting two ICPs counts once in bottom-up.
• Validate against sales reality: if win rate or ACV diverges, update SOM first.

Treat the analysis as a living document — refresh inputs quarterly and tie planning targets to the latest version.

Quarterly by default, with extra refreshes triggered by events:

1. Quarterly review — re-validate customer counts, pricing, and competitive share.
2. Product scope change — expansion or contraction shifts SAM (and sometimes TAM).
3. ICP change — tightening or broadening the profile changes count and conversion math.
4. Geographic expansion — new regions grow SAM but dilute SOM until mature.
5. Pricing change — even a test should roll into TAM and SOM immediately.
6. Fundraising cycle — stress-test inputs before each round for a consistent data-room story.

Between refreshes, keep assumption sources visible so anyone presenting can confirm the numbers still hold.