Market Sizing
Produce a rigorous TAM/SAM/SOM estimate that a PM can use in a pitch deck, strategy doc, or investment memo. The goal is defensible numbers with transparent assumptions — not inflated vanity metrics.
Process
- Define the market — Restate the input as a clear market definition: what product category, who is the buyer, what problem is being solved. Distinguish between the broad market and the specific segment.
- Research data points — Use WebSearch to find industry reports, public filings, analyst estimates, census data, and any credible source. Prioritize recent data (last 2 years). Note every source.
- Calculate TAM (Total Addressable Market) — Use top-down (industry report size) AND bottom-up (number of potential customers x average revenue per customer) if possible. If both methods yield different numbers, show both and explain the gap.
- Calculate SAM (Serviceable Addressable Market) — Apply geographic, segment, and capability filters. Be specific about what's excluded and why.
- Calculate SOM (Serviceable Obtainable Market) — Estimate realistic market capture in the first 1-3 years. Factor in competition, go-to-market approach, and growth benchmarks from comparable companies.
- Stress-test assumptions — Provide a range (conservative / base / optimistic) for at least SOM.
Output Format
Market Definition
One paragraph: what market, who buys, what problem, geographic scope.
TAM (Total Addressable Market)
Top-down: $X based on [source]. Calculation: [show the math]. Bottom-up: $X based on [number of customers] x [ARPU]. Calculation: [show the math]. Selected TAM: $X — [explain which estimate you trust more and why].
SAM (Serviceable Addressable Market)
Filters applied:
- Geographic: [filter]
- Segment: [filter]
- Other: [filter]
SAM: $X ([X%] of TAM). Calculation: [show the math].
SOM (Serviceable Obtainable Market)
| Scenario | SOM | Assumptions |
|---|---|---|
| Conservative | $X | ... |
| Base | $X | ... |
| Optimistic | $X | ... |
Methodology: [explain how you estimated capture rate — comparable company benchmarks, market share logic, etc.]
Key Assumptions
| # | Assumption | Impact if Wrong | Confidence |
|---|---|---|---|
| 1 | ... | ... | High/Med/Low |
| 2 | ... | ... | High/Med/Low |
Sources
Numbered list of every source used, with URLs when available.
Confidence Level
One paragraph: overall confidence in these numbers (High / Medium / Low) and what would increase confidence (e.g., "primary research with 20 target buyers would validate the ARPU assumption").
Rules
- Always show the math. Every number must trace back to a source or a calculation.
- Never use a single data point without cross-referencing. If only one source exists, flag it as low confidence.
- Bottom-up estimates are generally more trustworthy than top-down for niche markets. Say so when relevant.
- SOM should be grounded in reality: comparable company growth rates, typical market penetration for the GTM model, etc. Do not just pick an arbitrary percentage of SAM.
- Round numbers appropriately. Do not write "$4,237,891" — write "$4.2M". False precision erodes credibility.
- Write in English.
- Keep the entire output under 2 pages. Investors and execs skim — make every line count.
- Be opinionated: if the market is too small to build a venture-scale business, say so. If the sizing depends on a shaky assumption, call it out.
- If you cannot find reliable data for a critical input, flag it and provide a placeholder range rather than guessing.
