Market Sizing (TAM/SAM/SOM)
Overview
Market sizing quantifies the revenue opportunity in a market. The TAM/SAM/SOM framework provides progressively refined estimates from total market to realistically achievable share.
Required Frameworks
| Framework | Output Section | Required | Condition | |-----------|---------------|----------|-----------| | Methodology Selection | methodology rationale | yes | — | | TAM/SAM/SOM Hierarchy | Market Sizing Summary | yes | — | | Scenario Modeling | Scenarios | yes | — | | Growth Projections | CAGR/growth | yes | — |
Trend Indicators: Load and apply the trend indicator definitions from protocols/TREND-INDICATORS.md.
Key Definitions
TAM (Total Addressable Market)
- Total global market demand for a product/service
- Assumes 100% market share (theoretical maximum)
- Useful for understanding ceiling and investor conversations
SAM (Serviceable Addressable Market)
- Portion of TAM targetable with current business model
- Considers geographic, demographic, or segment constraints
- More realistic than TAM
SOM (Serviceable Obtainable Market)
- Realistic market share achievable in near term (1-3 years)
- Considers competition, resources, and go-to-market capability
- Most relevant for planning
Methodology Selection Guide
| User Signal | Recommended Methodology | |-------------|------------------------| | "TAM SAM SOM", "market opportunity", no pricing data | Top-Down | | Provides pricing, unit counts, or customer data | Bottom-Up | | Mentions "value", "pain point cost", "willingness to pay" | Value Theory | | "bottom-up" explicitly requested | Bottom-Up | | "growth trends", "CAGR", trend questions | Top-Down + Trend Analysis | | "bear/base/bull", "scenarios" | Any methodology + Scenario Modeling | | Vague with no segment specified | Top-Down (state assumptions) | | Market known to be declining | Top-Down + DEC trend handling |
Calculation Methodologies
Top-Down Approach
Start with large market data, narrow down:
- Find industry market size from analyst reports
- Apply relevant percentage for target segment
- Adjust for geography if not global
- Factor growth rates for projections
Example:
- Global SaaS market: $200B (TAM)
- HR SaaS segment: 15% → $30B (TAM refined)
- North America: 40% → $12B (SAM)
- Achievable share 2%: $240M (SOM)
Pros: Fast, uses existing research Cons: May miss nuances, depends on source quality
Bottom-Up Approach
Build from unit economics upward. When the user provides pricing data, use their exact figure:
- Identify target customer count — quantify the addressable customer base with specific numbers
- Estimate price per customer — use user-provided pricing if available; cite source otherwise
- Calculate total revenue potential — show the multiplication explicitly
Example:
- Target customers: 50,000 SMBs
- Average contract value: $5,000/year
- Total: $250M (SOM)
- Expand to all SMBs (500,000): $2.5B (SAM)
- Include enterprise: $10B (TAM)
Pros: More defensible, validates assumptions Cons: Slower, requires customer data
Value Theory Approach
Estimate based on value delivered (also called "willingness to pay" or "value-based" sizing):
- Calculate customer pain point cost — use the figure the user provides if given
- Estimate value of solution — what fraction of the pain does the tool address?
- Apply capture rate (typically 10-30% of value) — always state the percentage explicitly
- Still produce TAM/SAM/SOM — value theory informs pricing, but the output must maintain the three-tier structure
When the user provides a specific cost figure (e.g., "$4.5M per breach"), reference that exact number in the output and build the calculation around it.
Example:
- Customer loses $100K/year to problem
- Solution captures 20%: $20K willingness to pay
- 100,000 potential customers: $2B market
Trend Indicators
Apply three-valued logic to growth projections. Always include the Trend column in the Market Sizing Summary table.
- INC (Increasing): Market growing >10% annually
- CONST (Constant): Market growth 0-10% annually
- DEC (Decreasing): Market contracting (negative growth rates, show as
-X.X%)
Document evidence for each indicator — at minimum one analyst projection, adoption metric, or investment data point:
- INC: "Analyst projects 25% CAGR through 2027"
- CONST: "Mature market with 3% annual growth"
- DEC: "Legacy technology being displaced; revenue declined -12% YoY"
When the user asks about growth trends or CAGR specifically, expand the trend analysis with a sub-trend table breaking down growth by segment.
Data Sources
Primary Sources (Most Reliable):
- Industry analyst reports (Gartner, Forrester, IDC)
- Government statistics (Census, BLS)
- Trade association data
- Company financials (public companies)
Secondary Sources:
- Market research firms (Statista, IBISWorld)
- News articles citing research
- Industry publications
- Competitor disclosures
Estimation Sources (Use Carefully):
- LinkedIn job counts × average salary
- Google Trends relative volume
- App store downloads × price
- Website traffic estimates
Critical Output Requirements
Every market sizing output MUST include ALL of the following. Missing any of these is a failure:
- "Market Sizing Summary" header with a markdown table containing rows for TAM, SAM, and SOM
- Concrete dollar values (e.g.,
$18.5B,$240M) — NEVER use placeholder syntax like$X.XB,$XXM, or[insert value] - Methodology identification — explicitly state "Top-Down", "Bottom-Up", "Value Theory", or "Hybrid"
- "Key Assumptions" section with at least two numbered, specific assumptions
- "Data Sources" section referencing at least one named source
- "Confidence Level" section with High, Medium, or Low assessment and explanation
- TAM > SAM > SOM hierarchy — values must always follow this ordering
Handling Vague or Ambiguous Requests
When the user provides minimal context (e.g., "market size for drones"):
- State your scope assumptions explicitly — do not silently pick a segment
- Acknowledge market breadth — name the major segments (e.g., commercial, consumer, military)
- Still produce a TAM/SAM/SOM structure — even if the SOM must be conditional
- Ask clarifying questions at the end — suggest which details would refine the analysis
- Never return just a single number — always provide the full framework
Handling Declining Markets
When sizing a contracting market:
- Use DEC trend indicator and show negative growth rates (e.g.,
-12.5% CAGR) - Include a decline trajectory table showing year-over-year contraction
- Note risks and caveats specific to entering or operating in a declining market
- Still provide complete TAM/SAM/SOM — declining markets still have structure
- Include "Data Sources" section — declining market claims need backing
Output Structure
The output must follow this structure with REAL values (no placeholders):
## Market Sizing Summary
| Metric | Value | Growth | Trend |
|--------|-------|--------|-------|
| TAM | $18.5B | 15% CAGR | INC |
| SAM | $4.6B | 14% CAGR | INC |
| SOM | $92M | - | - |
## Methodology
Top-Down
## TAM Calculation
[Step-by-step derivation with cited sources and concrete numbers]
## SAM Derivation
[How SAM was narrowed from TAM with specific percentages]
## SOM Justification
[Realistic share rationale with customer count or market share basis]
## Key Assumptions
1. Market growth rate of 15% CAGR sustained through 2028; if growth slows to 10%, TAM drops to $3.2B
2. Target segment represents 35% of total market based on [source]
## Data Sources
- Gartner (2024): Market size and growth projections
- Census Bureau: Demographic data for customer count
## Confidence Level
Medium — Single methodology with multiple supporting data points. Would upgrade to High with bottom-up corroboration.
Validation Rules
Before finalizing output, verify:
- Hierarchy check: TAM > SAM > SOM — if this fails, re-examine your filtering logic
- No placeholders: Search output for
$X,[insert,[Assumption,$XXM,TBD— replace all with concrete values - User input echo: If the user provided a price point, cost figure, or other specific data, that exact value MUST appear in the output
- Methodology match: If the user requested a specific methodology (bottom-up, value theory), the output must identify that methodology by name
- Trend evidence: If trend indicators (INC/CONST/DEC) are used, at least one supporting data point must follow
Common Pitfalls
- Double-counting: Ensure segments don't overlap
- Currency confusion: Specify USD/EUR and year
- Stale data: Note data age, adjust for growth
- Over-optimism: SOM should be conservative
- Missing context: Include methodology for credibility
- Template residue: Never leave template placeholders in final output —
$X.XBor[Source 1]in the output is a failure
Scenario Modeling
When the user requests scenarios (bear/base/bull), provide a range. The values MUST satisfy Bear < Base < Bull for every metric (TAM, SAM, SOM). Each scenario must include a rationale explaining its key drivers.
| Scenario | TAM | SAM | SOM | |----------|-----|-----|-----| | Bear | $5B | $500M | $10M | | Base | $8B | $800M | $25M | | Bull | $12B | $1.2B | $50M |
Never use placeholder values ($X, $X.XB, [insert], [Assumption) in scenario tables — use concrete dollar amounts.
Quality Checklist
Before delivering the output, mentally verify:
- [ ] "Market Sizing Summary" table is present with TAM, SAM, SOM rows
- [ ] All dollar values are concrete (no
$X.XBpatterns) - [ ] TAM > SAM > SOM holds numerically
- [ ] Methodology is named explicitly
- [ ] Key Assumptions has at least 2 numbered items
- [ ] Data Sources names at least 1 real source
- [ ] Confidence Level states High/Medium/Low
- [ ] If user gave pricing/cost data, it appears verbatim in the output
- [ ] If scenarios requested, Bear < Base < Bull for all metrics
- [ ] If declining market, negative growth rate shown and risks noted
Additional Resources
For detailed templates and examples, see:
references/sizing-methodologies.md- Complete methodology guidereferences/data-sources.md- Source reliability ratingsexamples/market-sizing-report.md- Sample sizing report
Orchestration Hints
Confidence tiers (universal scale):
- High: 3+ independent, recent (<12mo) sources that converge
- Medium: 2 sources OR sources >12mo old OR indirect evidence
- Low: Single source, inference, or extrapolation
Dimension-specific confidence criteria below REFINE (not replace) these universal definitions.
- Cross-reference dimensions: financial (revenue validation), competitive (player count and share)
- Alert triggers:
- TAM deviation >30% from initial expectations
- Growth rate reversal (INC→DEC or vice versa)
- Segment emerging that wasn't in original scope
- Confidence rules:
- High: Top-down and bottom-up estimates converge within 20%
- Medium: Single methodology with 2+ supporting data points
- Low: Single data point or significant methodology gaps
- Conflict detection:
- Sum of competitor revenues vs total market size
- Growth projections vs trend dimension's macro indicators
- Segment sizes vs customer dimension's adoption estimates