TL;DR

TAM, SAM, and SOM are the three layers of market sizing. Most companies calculate them incorrectly — using top-down analyst estimates instead of bottom-up calculations. A credible market sizing analysis is built from unit economics, not market research reports.

The Three Layers of Market Size

TAM (Total Addressable Market): Total revenue opportunity if you captured 100% of the market

SAM (Serviceable Addressable Market): Portion of TAM your product can actually serve given current capabilities, geography, and GTM

SOM (Serviceable Obtainable Market): Portion of SAM you can realistically capture in 3–5 years given resources and competitive position

Top-Down vs. Bottom-Up

Top-down: Start with a large market estimate and apply a percentage. "The global CRM market is $50B. We will capture 1% = $500M." NOT CREDIBLE.

Bottom-up: Start with the number of potential customers and multiply by revenue per customer. "There are 500,000 mid-market companies in North America. 20% are relevant (100,000). At $10,000 ACV, our SAM is $1B." ALWAYS MORE CREDIBLE.

Step-by-Step Market Sizing

Step 1: Define your customer unit — who is the buyer? (company, department, individual)

Step 2: Count the universe — use US Census Bureau, LinkedIn, industry associations, INEGI (Mexico), BLS (US)

Step 3: Apply relevance filters — what % of the universe has the problem you solve? (ICP filters)

Step 4: Calculate revenue per unit — ACV or revenue per customer per year

Step 5: Calculate TAM/SAM/SOM:

  • TAM = Total universe × ACV
  • SAM = Filtered universe (ICP-qualified) × ACV
  • SOM = SAM × realistic market share (typically 1–5% in year 3–5)

Common Mistakes

  1. Using analyst reports without bottom-up validation
  2. Confusing TAM and SAM — TAM is theoretical. SAM is what you can actually sell to
  3. Overstating SOM — claiming 10%+ market share in 3 years is rarely credible

4. Ignoring geographic constraints

Key Takeaways

Key Takeaways
  • Bottom-up market sizing is always more credible than top-down.
  • TAM is theoretical; SAM is what you can serve; SOM is what you can win.
  • Build from unit economics: number of customers × ACV.
  • Apply ICP filters to narrow TAM to SAM.
  • SOM of 1–5% of SAM in 3–5 years is typically credible.