TAM SAM SOM: A Practical Guide for Product Teams

Why Market Sizing Matters

Market sizing isn't just for pitch decks and board meetings. When done right, it answers a fundamental product question: How big is the opportunity we're going after?

The Framework

• TAM (Total Addressable Market) — The entire revenue opportunity if you captured 100% of the market
• SAM (Serviceable Addressable Market) — The portion you can realistically reach with your current business model
• SOM (Serviceable Obtainable Market) — What you can actually capture in the near term

Top-Down vs Bottom-Up

Most teams default to top-down sizing: "The global CRM market is $80B, we'll capture 1%." This is lazy and almost always wrong.

Bottom-up is better:

Potential customers in your segment × Average deal size × Win rate = SOM

For example:

• 5,000 mid-market SaaS companies (your ICP)
• $24,000 average annual contract
• 5% realistic win rate in year 1
• SOM = $6M

That's a lot more honest than "$800M TAM, we just need 0.1%."

Triangulation

The best approach uses multiple methods and triangulates:

1. Top-down: Industry reports, analyst data, public market research
2. Bottom-up: Customer count × ARPU calculations
3. Competitive: Sum of competitor revenues + estimated whitespace

If all three methods converge on a similar range, you have a defensible number.

Common Mistakes

• Defining the market too broadly ("all software")
• Ignoring geographic or segment constraints
• Using 5-year-old data without adjusting for growth
• Confusing TAM with SAM (the most common error)

Make It Actionable

A market size is only useful if it informs decisions:

• Is this market big enough to support our ambitions?
• Which segment should we enter first?
• How does our pricing map to the opportunity?
• Where are competitors leaving money on the table?

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Ossia's Market Sizer automates this entire process — triangulating TAM/SAM/SOM using AI-powered research across top-down, bottom-up, and competitive approaches.