market-sizing

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

1. 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.
2. 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.
3. 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.
4. Calculate SAM (Serviceable Addressable Market) — Apply geographic, segment, and capability filters. Be specific about what's excluded and why.
5. 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.
6. 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.