Market Sizing — TAM/SAM/SOM Calculator

Calculate defensible TAM, SAM, and SOM market sizes using top-down and bottom-up methods with source citations for pitches and business cases.

Build defensible market sizing for any product, pitch deck, or business case. Top-down and bottom-up methodologies combined.

What You Get

• TAM (Total Addressable Market) — entire market if you had 100% share
• SAM (Serviceable Addressable Market) — segment you can actually reach
• SOM (Serviceable Obtainable Market) — realistic capture in 12-36 months
• Bottom-up validation — unit economics × reachable customers
• Source citations — government data, industry reports, public filings

How to Use

Tell me your product/service and target customer. I'll build the full sizing.

Example prompts:

• "Size the market for AI-powered contract review for mid-market law firms in the US"
• "TAM/SAM/SOM for a SaaS helpdesk targeting e-commerce brands doing $1M-$50M revenue"
• "Market size for automated bookkeeping for UK SMBs"

Methodology

Top-Down

1. Start with total industry revenue (cite source)
2. Filter by geography, segment, company size
3. Apply technology adoption rates
4. Result = SAM

Bottom-Up

1. Count reachable customers (databases, directories, LinkedIn)
2. Multiply by realistic ACV (annual contract value)
3. Apply conversion rates at each funnel stage
4. Result = SOM

Triangulation

Compare top-down and bottom-up. If they're within 2-3x of each other, the sizing holds. If wildly different, investigate assumptions.

Output Format

text

## Market Sizing: [Product/Service]

### TAM — $X.XB
[Total market calculation with sources]

### SAM — $XXM
[Filtered by geography + segment + tech adoption]

### SOM (12-month) — $X.XM
[Bottom-up: customers × ACV × conversion]

### Key Assumptions
- [Assumption 1 + source]
- [Assumption 2 + source]

### Risks to Sizing
- [What could make this smaller]
- [What could make this bigger]

When to Use This

• Pitch decks and investor presentations
• Go-to-market strategy planning
• New product feasibility analysis
• Board presentations and business cases
• Competitive positioning

Pro Tip

Most founders oversize their TAM and undersize their SOM. Investors see through inflated numbers instantly. A tight, well-sourced $50M SAM beats a hand-wavy $10B TAM every time.

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