Rigorous market sizing using dual TAM/SAM/SOM methodology (top-down and bottom-up) with reconciliation, sensitivity analysis, and growth projection.
Required Inputs
| Input | Description | Required? |
|---|---|---|
| Industry / product category | What market is being sized | Yes |
| Geographic scope | Country, region, or global | Yes |
| Target customer segment(s) | Who buys this product/service | Yes |
| Product/service definition | What is being sold, at what price point | Yes |
| Time horizon | Current year and projection period (e.g., 2026-2031) | Yes |
| Company capabilities | Current reach, channels, capacity constraints | For SOM |
| Known data points | Any existing research, revenue figures, customer counts | If available |
| Currency | Reporting currency | Yes |
Execution Steps
Step 1: Define Market Boundaries
Establish precise definitions before any calculation:
- Product scope: What products/services are included and excluded?
- Customer scope: Which buyer segments (B2B, B2C, enterprise, SMB)?
- Geographic scope: Which countries/regions? Regulatory differences?
- Value chain scope: Which parts of the value chain (manufacturing, distribution, SaaS layer)?
Document boundary decisions explicitly — these are the #1 source of market sizing disagreements.
Step 2: Top-Down Analysis
Start from the largest defensible number and narrow:
-
Identify macro data sources (in order of reliability):
- Government statistics (Census, BLS, Eurostat, national statistical offices)
- Industry association reports (trade bodies, industry groups)
- Analyst reports (Gartner, IDC, Forrester, Statista, IBISWorld)
- Public company filings (10-K revenue disclosures, earnings calls)
- Academic research and published studies
-
Calculate top-down TAM:
- Total industry revenue globally or in target geography
- OR: Total number of potential buyers x average annual spend per buyer
-
Apply segmentation filters for SAM:
- Filter by geography served
- Filter by customer segment targeted
- Filter by product/service fit (what portion of spend your offering addresses)
- Filter by channel accessibility
-
Apply penetration and capacity constraints for SOM:
- Realistic market share given competitive landscape (use analogues)
- Channel and sales capacity limits
- Brand awareness and reach constraints
- Time-to-penetrate considerations
Step 3: Bottom-Up Analysis
Build from unit economics upward:
-
Count target customers:
- Identify the number of potential buyers in each segment
- Use company registries, industry databases, demographic data
-
Estimate purchase behavior:
- Average deal size / ticket price
- Purchase frequency (annual, monthly, one-time)
- Adoption rate by segment (early adopters vs. mainstream)
-
Calculate bottom-up TAM:
TAM = Σ (Customers_in_segment × Price × Purchase_frequency) for all segments -
Calculate bottom-up SAM:
SAM = Σ (Reachable_customers × Price × Frequency) for served segments -
Calculate bottom-up SOM:
SOM = SAM × Expected_penetration_rate × Conversion_rate
Step 4: Reconciliation
Compare top-down and bottom-up estimates:
- Calculate variance: If top-down and bottom-up differ by >30%, investigate why
- Identify discrepancy sources:
- Pricing assumptions differ?
- Customer count estimates differ?
- Scope definitions misaligned?
- Triangulate: Use a third method (e.g., analogue-based, value-theory) if gap persists
- Select final estimate: State which approach is primary and why; use the other as a sanity check
- Document confidence level: High (estimates within 15%), Medium (15-40% range), Low (>40% range)
Step 5: Growth Rate Projection
Project market growth over the time horizon:
- Historical growth rate: CAGR over last 3-5 years from industry data
- Driver-based growth model:
- Population/business formation growth
- Penetration rate increase (adoption curve position)
- Price changes (inflation, premiumization, commoditization)
- Usage intensity changes
- Regulatory tailwinds/headwinds
- Analogue comparison: How did similar markets grow? (e.g., cloud adoption curve for AI SaaS)
- Adoption curve positioning: Where on the S-curve is this market? (innovators → early majority → late majority)
| Growth Phase | Typical Annual Growth | Characteristics |
|---|---|---|
| Emerging | 30-80%+ | Pre-product/market fit, few players |
| High growth | 15-30% | Product/market fit proven, competition entering |
| Growth | 8-15% | Market maturing, consolidation beginning |
| Mature | 2-8% | Established players, GDP+ growth |
| Declining | <0% | Substitution, obsolescence |
Step 6: Sensitivity Analysis
Test key assumptions:
- Identify the 3-5 variables with the highest impact on market size (typically: customer count, price, adoption rate, growth rate)
- Define ranges for each variable (pessimistic, base, optimistic)
- Build sensitivity table: Show how TAM/SAM/SOM change as each variable moves
- Tornado chart inputs: Rank variables by impact magnitude
Output Template
Market Sizing: [Industry/Product] — [Geography]
Date: [Date] | Prepared for: [Client/Project] | Confidence Level: [High/Medium/Low]
1. Market Definition & Boundaries
| Dimension | Included | Excluded |
|---|---|---|
| Products/Services | [Specific offerings] | [Adjacent categories excluded] |
| Customer Segments | [Target segments] | [Non-target segments] |
| Geographies | [Countries/regions] | [Out-of-scope regions] |
| Value Chain | [Stages included] | [Stages excluded] |
2. TAM / SAM / SOM Waterfall
| Metric | Top-Down Estimate | Bottom-Up Estimate | Reconciled Estimate | Confidence |
|---|---|---|---|---|
| TAM (Total Addressable Market) | $[X]B | $[X]B | $[X]B | [H/M/L] |
| SAM (Serviceable Addressable Market) | $[X]B | $[X]B | $[X]B | [H/M/L] |
| SOM (Serviceable Obtainable Market) | $[X]M | $[X]M | $[X]M | [H/M/L] |
SAM as % of TAM: [X]% — [Explanation of narrowing factors] SOM as % of SAM: [X]% — [Explanation of capture assumptions]
3. Top-Down Methodology
| Step | Value | Source | Notes |
|---|---|---|---|
| Global industry revenue | $[X]B | [Source, Year] | [Methodology note] |
| Geographic filter ([Region]) | $[X]B | [Source] | [X]% of global |
| Segment filter ([Segment]) | $[X]B | [Source] | [X]% of regional |
| Product relevance filter | $[X]B | [Assumption] | [X]% of segment spend |
| Top-Down TAM | $[X]B |
4. Bottom-Up Methodology
| Segment | # of Customers | Avg. Annual Spend | Segment TAM |
|---|---|---|---|
| [Segment 1] | [N] | $[X] | $[X]M |
| [Segment 2] | [N] | $[X] | $[X]M |
| [Segment 3] | [N] | $[X] | $[X]M |
| Total Bottom-Up TAM | [N] | $[X] avg | $[X]B |
5. Reconciliation
| Approach | TAM | SAM | SOM | Variance vs. Reconciled |
|---|---|---|---|---|
| Top-Down | $[X]B | $[X]B | $[X]M | [+/-X]% |
| Bottom-Up | $[X]B | $[X]B | $[X]M | [+/-X]% |
| Reconciled | $[X]B | $[X]B | $[X]M | — |
Reconciliation notes: [Explain why one approach is favored, what drove differences, how you resolved them]
6. Market Growth Projection
| Year | TAM | Growth % | SAM | SOM |
|---|---|---|---|---|
| [Current] | $[X]B | — | $[X]B | $[X]M |
| [+1] | $[X]B | [X]% | $[X]B | $[X]M |
| [+2] | $[X]B | [X]% | $[X]B | $[X]M |
| [+3] | $[X]B | [X]% | $[X]B | $[X]M |
| [+5] | $[X]B | [X]% | $[X]B | $[X]M |
Growth CAGR ([Current]-[+5]): TAM [X]% | SAM [X]% | SOM [X]%
Key growth drivers:
- [Driver 1 — quantified impact]
- [Driver 2 — quantified impact]
- [Driver 3 — quantified impact]
7. Sensitivity Analysis
Tornado Chart — Impact on TAM (Base: $[X]B)
| Variable | Low Case | Base Case | High Case | TAM Range |
|---|---|---|---|---|
| [Variable 1] | [Low] | [Base] | [High] | $[X]B - $[X]B |
| [Variable 2] | [Low] | [Base] | [High] | $[X]B - $[X]B |
| [Variable 3] | [Low] | [Base] | [High] | $[X]B - $[X]B |
| [Variable 4] | [Low] | [Base] | [High] | $[X]B - $[X]B |
Combined scenario range: $[Low]B (pessimistic) → $[Base]B (base) → $[High]B (optimistic)
8. Data Sources & Confidence Assessment
| Data Point | Source | Year | Confidence | Risk |
|---|---|---|---|---|
| [Data point 1] | [Source] | [Year] | [H/M/L] | [Key risk to accuracy] |
| [Data point 2] | [Source] | [Year] | [H/M/L] | [Key risk to accuracy] |
9. Key Assumptions & Caveats
- [Assumption 1 — impact if wrong]
- [Assumption 2 — impact if wrong]
- [Assumption 3 — impact if wrong]
Quality Checks
- TAM, SAM, and SOM are each calculated using BOTH top-down and bottom-up approaches
- Top-down and bottom-up estimates are reconciled with variance explained
- Every data point cites a specific source with year
- Market boundaries (product, geography, customer, value chain) are explicitly defined
- SAM narrowing from TAM is explained with specific filters and percentages
- SOM includes realistic penetration assumptions, not aspirational targets
- Growth projections use driver-based methodology, not just trend extrapolation
- Sensitivity analysis tests at least 3 key variables with defined ranges
- Confidence level (High/Medium/Low) is stated for each major estimate
- Currency, time period, and geographic scope are stated in every table header
- No circular reasoning (not using own revenue targets to justify market size)
- Sanity checks applied: per-capita spend, comparison to adjacent markets, public company revenue benchmarks