~2 min read
TAM, SAM, and SOM define your market opportunity at three levels of specificity. Every investor deck needs these numbers, and how you define them signals whether you understand your market.
The three levels
TAM (Total Addressable Market): The total global revenue opportunity if you captured 100% of the market. This is a ceiling — not a realistic target.
SAM (Serviceable Addressable Market): The portion of TAM you can realistically serve given your product's current capabilities, geographic reach, and go-to-market.
SOM (Serviceable Obtainable Market): The portion of SAM you can realistically capture in 3–5 years, given competition and your go-to-market scale.
Top-down vs bottom-up market sizing
Top-down: Industry reports estimate total market size, and you identify your percentage. Fast, but imprecise. "The CRM market is $50B, and we target 1%."
Bottom-up: Count actual customers and multiply by ACV. More credible. "There are 500,000 mid-market companies in the US, 30% have this problem, we can reach 15% of those with our current GTM (go-to-market), at $15k ACV = $337M SAM."
Investors prefer bottom-up because it shows you understand the actual customer pool.
Investor expectations by stage
| Stage | Minimum TAM | Notes |
|---|---|---|
| Seed | $500M | VCs need headroom for a $50M+ outcome |
| Series A | $1B+ | Fund math requires large market potential |
| Series B+ | $5B+ | To justify growth at scale and IPO narrative |
TAM below $500M is not automatically disqualifying — services businesses and vertical SaaS can build highly profitable $50–100M revenue businesses in smaller markets. But VC-backed hypergrowth requires massive markets.
Common mistakes in market sizing
Overcounting TAM: "The global enterprise software market is $500B, we're in software, therefore our TAM is $500B." Wrong. TAM must be the market for your specific product category.
Confusing TAM and SAM: "Our SAM is the entire US market." SAM should filter by who you can actually sell to today — your ICP, not the entire country.
Unrealistic SOM: "We'll capture 10% of the market in year 3." Without showing the GTM math (headcount, channels, CAC), this is unbelievable.
Frequently asked questions
What does this calculator do? Calculate TAM (total customers × spend), SAM (filtered by your reach), and SOM (your achievable share) for market sizing in investor decks.