Almost every AI pitch deck has the same slide. A huge number, a market research firm's logo, and a line like "the AI market will be worth trillions." Investors skip it. It tells them nothing about your business, because you aren't selling "AI". You're selling a specific job done for a specific customer at a specific price.
This guide shows how to size that instead. If you need a refresher on the definitions first, start with our TAM vs SAM vs SOM guide.
The three numbers, in one line each
- TAM (total addressable market) — the revenue you'd make if every possible customer bought your product at your price.
- SAM (serviceable addressable market) — the part of TAM your product, channel and geography can actually serve today.
- SOM (serviceable obtainable market) — the part of SAM you can realistically win in the next 3–5 years, given your team and go-to-market.
The rule that matters for AI startups: build all three from the bottom up — number of customers × price per customer — and use top-down reports only as a sanity check.
Worked example: an AI receptionist for dental offices
Imagine an AI that answers a dental office's phone, books appointments into the practice's software, and handles calls after hours. Here's how to size it.
Step 1: Count the customers
The buyer is the dental office, not the dentist. The US Census Bureau's County Business Patterns data lists about 135,000 dental office establishments with employees (NAICS 621210, 2023). As a cross-check, the American Dental Association counts about 200,000 practising dentists, which fits with many offices having more than one dentist.