How to calculate TAM, SAM, and SOM for a B2B startup
TAM, SAM, and SOM are market sizing frameworks every B2B founder needs for investor conversations and strategic planning. TAM is the total market. SAM is the segment you can serve. SOM is what you can realistically capture in the near term. Here's how to calculate each correctly.
TAM (Total Addressable Market), SAM (Serviceable Addressable Market), and SOM (Serviceable Obtainable Market) are the three layers of market sizing every B2B founder needs. TAM is the total revenue opportunity if you captured the entire market. SAM is the portion you can realistically serve with your current product and model. SOM is what you can actually capture in the next 1–3 years. Investors use these numbers to evaluate whether the market is large enough to justify the company. Founders use them to prioritise where to focus.
How do you calculate TAM?
Top-down: start from a market research figure for the total industry size and work down. Bottom-up (more credible): count the total number of companies in your target market and multiply by your ACV. Example: if there are 500,000 B2B SaaS companies with 10–200 employees globally, and your product would price at $10,000/year for each, the TAM is $5B. Bottom-up TAM calculations are more defensible because they show your work. Top-down figures from market research reports are often too broad to be meaningful.
How do you calculate SAM?
SAM is the portion of TAM you can actually serve — bounded by your product's current capabilities, the geographies you serve, and the segments you're targeting. If your product currently only works well for English-speaking markets and requires a certain minimum company size to get value, your SAM is the subset of TAM that fits those criteria. Example: of the 500,000 companies in the TAM, 120,000 are in English-speaking markets with 20–200 employees — SAM is $1.2B.
How do you calculate SOM?
SOM is what you can realistically capture in 3–5 years given your current resources. There's no formula — it's a reasonable estimate based on your current growth rate, sales capacity, and market penetration. Common approach: how many customers can your sales team close per year at your current scale? What does that look like compounded over 3 years with some team growth? If you can close 200 new customers per year today and grow that 50% annually, your SOM over 3 years is roughly 600–800 customers — at $10K ACV, that's $6–8M ARR.
What do investors actually care about in market sizing?
That the TAM is large enough to build a venture-scale company — typically $1B+ for investors looking for 10x returns. That the SAM is defensible — not the whole TAM, but a specific segment you can win. And that the SOM shows you understand your near-term constraints. The mistake founders make: citing huge TAM numbers from analyst reports without the bottom-up calculation. "The CRM market is $100B" doesn't tell an investor whether there's a real market for your specific product.