Market Sizing

Rigorous market sizing using dual TAM/SAM/SOM methodology (top-down and bottom-up) with reconciliation, sensitivity analysis, and growth projection.

Required Inputs

Execution Steps

Step 1: Define Market Boundaries

Establish precise definitions before any calculation:

1. Product scope: What products/services are included and excluded?
2. Customer scope: Which buyer segments (B2B, B2C, enterprise, SMB)?
3. Geographic scope: Which countries/regions? Regulatory differences?
4. 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:

1. 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

1. Calculate top-down TAM:

- Total industry revenue globally or in target geography - OR: Total number of potential buyers x average annual spend per buyer

1. 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

1. 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:

1. Count target customers:

- Identify the number of potential buyers in each segment - Use company registries, industry databases, demographic data

1. Estimate purchase behavior:

- Average deal size / ticket price - Purchase frequency (annual, monthly, one-time) - Adoption rate by segment (early adopters vs. mainstream)

1. Calculate bottom-up TAM:

`` TAM = Σ (Customersinsegment × Price × Purchase_frequency) for all segments ``

1. Calculate bottom-up SAM:

`` SAM = Σ (Reachable_customers × Price × Frequency) for served segments ``

1. Calculate bottom-up SOM:

`` SOM = SAM × Expectedpenetrationrate × Conversion_rate ``

Step 4: Reconciliation

Compare top-down and bottom-up estimates:

1. Calculate variance: If top-down and bottom-up differ by >30%, investigate why
2. Identify discrepancy sources:

- Pricing assumptions differ? - Customer count estimates differ? - Scope definitions misaligned?

1. Triangulate: Use a third method (e.g., analogue-based, value-theory) if gap persists
2. Select final estimate: State which approach is primary and why; use the other as a sanity check
3. 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:

1. Historical growth rate: CAGR over last 3-5 years from industry data
2. 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

1. Analogue comparison: How did similar markets grow? (e.g., cloud adoption curve for AI SaaS)
2. Adoption curve positioning: Where on the S-curve is this market? (innovators → early majority → late majority)

Step 6: Sensitivity Analysis

Test key assumptions:

1. Identify the 3-5 variables with the highest impact on market size (typically: customer count, price, adoption rate, growth rate)
2. Define ranges for each variable (pessimistic, base, optimistic)
3. Build sensitivity table: Show how TAM/SAM/SOM change as each variable moves
4. 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

2. TAM / SAM / SOM Waterfall

SAM as % of TAM: [X]% — [Explanation of narrowing factors] SOM as % of SAM: [X]% — [Explanation of capture assumptions]

3. Top-Down Methodology

4. Bottom-Up Methodology

5. Reconciliation

Reconciliation notes: [Explain why one approach is favored, what drove differences, how you resolved them]

6. Market Growth Projection

Growth CAGR ([Current]-[+5]): TAM [X]% | SAM [X]% | SOM [X]%

Key growth drivers:

1. [Driver 1 — quantified impact]
2. [Driver 2 — quantified impact]
3. [Driver 3 — quantified impact]

7. Sensitivity Analysis

Tornado Chart — Impact on TAM (Base: $[X]B)

Combined scenario range: $[Low]B (pessimistic) → $[Base]B (base) → $[High]B (optimistic)

8. Data Sources & Confidence Assessment

9. Key Assumptions & Caveats

1. [Assumption 1 — impact if wrong]
2. [Assumption 2 — impact if wrong]
3. [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