What Are TAM, SAM and SOM?
TAM, SAM and SOM are three nested ways to size a market: total demand, the part your product could serve, and the realistic share you can capture soon.
How it works
TAM (total addressable market) is the total revenue available if everyone who could use your type of product bought it. SAM (serviceable addressable market) is the slice you can actually reach with your product, location and pricing. SOM (serviceable obtainable market) is the share of that slice you can realistically win in the near term, given competition and your resources.
Top-down vs bottom-up
A top-down estimate starts from a big industry figure and narrows it. A bottom-up estimate starts from unit economics: how many customers you can reach times what each pays. Bottom-up is usually more credible because every input is something you can check.
Example
For example, say you sell scheduling software to independent dental practices in the US. Bottom-up: assume 100,000 practices (a hypothetical figure) and a price of $2,000 a year. TAM is 100,000 x $2,000 = $200 million. If you only serve practices with two to five dentists, perhaps 40,000 of them, SAM is $80 million. If you can credibly win 2% of SAM in three years, SOM is $1.6 million. Replace each number with researched data before using it.
Why founders care
Investors want to know that the market can support a large business, and you need to know whether the market can support yours at all. Sizing also forces you to define your first customer clearly. It feeds directly into a pitch deck and your go-to-market strategy.
Common mistakes
- The "1% of a huge market" trap. Saying you need only 1% of a billion-dollar market is not a plan.
- Counting everyone as a customer when many would never buy.
- Using only top-down numbers from a report you cannot verify.
- Ignoring pricing. Your market size depends on what customers will actually pay.
Frequently asked questions
What is the difference between TAM, SAM and SOM?
TAM is the total revenue opportunity for your type of product. SAM is the part of it your product, geography and pricing can serve. SOM is the portion you can realistically capture in the near term against competitors.
How do you calculate TAM?
Top-down: take an industry total and narrow it by relevant filters. Bottom-up: multiply the number of potential customers by the average yearly revenue per customer. Bottom-up is generally easier to defend because each input can be checked.
Related terms
Go deeper
- Pitch Deck Outline: What to Include, Slide by Slide GuideA pitch deck outline for first-time founders: what goes on each slide, how to order them, seed pitch deck tips and the mistakes that sink an investor deck.
- How to Validate a Startup Idea Before You Build GuideHow to validate a startup idea before you build it: customer interviews, a question bank, landing page tests, and a checklist for deciding whether to go ahead.
- How to Write a Business Plan: Template and Steps GuideHow to write a business plan for a startup: a section-by-section template, a lean one-page version, and what changes when the reader is an investor or a bank.
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General information, not legal, tax or financial advice. Reviewed 11 November 2026.