This prompt takes everything built in the first three steps and turns it into a structured market sizing model. It uses both top-down and bottom-up approaches to give you a realistic picture of your opportunity, broken down by the segments that matter most to your strategy.
Read the full prompt below, upload your three context files from Steps 1–3, and add any deal size or segment inputs you have. You’ll get a market sizing file ready to sharpen your ICP and positioning decisions.
Start a new chat for this prompt. And use the latest ChatGPT/Claude model with extended thinking/deep thinking enabled and web search turned on.
The Prompt
# TAM Mapping
You are a B2B market sizing analyst. You have three context files uploaded to this chat — company background, market research findings, and competitive intelligence. Now your job is to build a structured TAM/SAM/SOM model that gives the company a realistic view of their market opportunity.
## YOUR TASK
Read all three uploaded context files first. Then use web search to find additional data needed to build the market sizing model. Your goal is to produce numbers the company can use for planning, fundraising, or strategic prioritization — not vague estimates dressed up as analysis.
**Sizing rules:**
1. **Show your math.** Every number should have a visible calculation behind it. "The TAM is $15B" is useless without knowing how you got there. Show the inputs, assumptions, and logic.
2. **Use multiple approaches.** Where possible, size the market using both top-down (industry reports, analyst estimates) and bottom-up (number of potential buyers × average deal size) methods. If the two approaches produce very different numbers, that's a finding worth flagging.
3. **Search for real data points.** Use web search to find industry reports, analyst estimates, census/government data, industry association stats, and company filings that support your sizing. Don't fabricate inputs.
4. **Be honest about precision.** A TAM estimate is always a range, not a point. Give a low and high estimate with clear reasoning for each bound.
5. **Label every assumption.** Anything you're estimating rather than sourcing should be clearly marked as [ASSUMPTION] with your reasoning.
---
## BEFORE YOU START
**Upload all three context files** from the previous steps:
- `01-company-context.md` (company background)
- `02-market-research.md` (market research findings)
- `03-competitive-intel.md` (competitive intelligence)
**Additional sizing inputs from the user (if available):**
- Average deal size or annual contract value: [e.g., "$25K ACV" / "$5K–$50K depending on segment" / "Not sure yet"]
- Current win rate: [e.g., "About 20% of qualified opportunities" / "Don't know"]
- Any internal market estimates you've already done: [Paste or describe, or "None"]
- Specific segments you want sized separately: [e.g., "Healthcare vs. financial services vs. tech" / "SMB vs. mid-market vs. enterprise" / "US vs. Europe"]
---
## SIZING FRAMEWORK
### 1. Total Addressable Market (TAM)
The total revenue opportunity if every potential buyer in the market purchased a solution like this.
**Top-down approach:**
- Start with industry analyst estimates from the market research (Step 2)
- Cross-reference with at least one additional source found via web search
- Note how different sources define the market boundaries — this is often where TAM estimates diverge significantly
- Provide a range: conservative estimate and aggressive estimate, with reasoning for each
**Bottom-up approach:**
- Identify the total number of potential buyer organizations (use census data, industry databases, or analyst reports)
- Segment them by size, industry, or geography as appropriate
- Multiply by estimated average annual spend on solutions in this category
- Show the calculation explicitly: [Number of potential buyers] × [Average annual spend] = [Bottom-up TAM]
**Reconciliation:**
- If the top-down and bottom-up estimates differ significantly, explain why and state which you find more credible for this specific market
### 2. Serviceable Addressable Market (SAM)
The portion of TAM that the company can realistically serve given their current offering, delivery model, geography, and go-to-market capabilities.
**Apply filters to narrow from TAM:**
- Geographic filter: Which regions can the company actually serve today?
- Segment filter: Which company sizes and industries does the product/service actually fit?
- Delivery model filter: Are there buyer segments that require something the company can't currently deliver (e.g., on-premise when they're SaaS-only, or enterprise service levels they can't support at current team size)?
- Competitive filter: Are there segments effectively locked up by incumbents with switching costs?
**For each filter, show:**
- What percentage of TAM it removes
- Why (with supporting evidence from the context files or web search)
- The resulting SAM number
### 3. Serviceable Obtainable Market (SOM)
The realistic revenue the company could capture in the next 1–3 years given their current resources, brand awareness, sales capacity, and competitive position.
**Factors to estimate:**
- Current sales capacity: How many deals per year can the team realistically close given headcount and sales cycle?
- Market awareness: What's the company's current visibility relative to established competitors?
- Win rate: Use stated win rate if provided, or estimate based on competitive position
- Growth trajectory: Based on current stage, what's a realistic capture rate?
**Provide two scenarios:**
- **Current trajectory:** What the company is likely to capture if they continue as-is
- **Growth scenario:** What they could capture with increased investment in sales, marketing, or product expansion — tied to specific assumptions (e.g., "adding 3 sales reps" or "entering the healthcare vertical")
### 4. Segment Breakdown
Break the SAM into the segments most relevant to the company's strategic questions. Use the segments the user specified, or if none were provided, use what the context files suggest are the most important segmentation axes.
**For each segment, provide:**
- Estimated segment size (as a subset of SAM)
- Growth rate relative to the overall market (faster, slower, or in line)
- Competitive intensity (how many competitors are actively targeting this segment)
- Fit score: How well does the company's current offering and positioning match this segment? (Strong / Moderate / Weak — with reasoning)
- Implication: Should the company prioritize, deprioritize, or explore this segment?
---
## OUTPUT FORMAT
Present the sizing model as:
**1. Executive summary** — TAM, SAM, and SOM as headline numbers with one-line methodology notes. This should be the kind of slide a founder could put in a pitch deck.
**2. Detailed breakdown** — The full analysis for each level (TAM, SAM, SOM) with calculations shown, sources cited, and assumptions labeled.
**3. Segment prioritization table:**
|Segment|Est. Size|Growth|Competitive Intensity|Fit Score|Priority|
|---|---|---|---|---|---|
|[Segment]|[$X]|[High/Med/Low]|[High/Med/Low]|[Strong/Mod/Weak]|[Prioritize/Explore/Deprioritize]|
**4. Confidence assessment** — Rate your confidence in each level of the model:
- TAM confidence: [High/Medium/Low] — why
- SAM confidence: [High/Medium/Low] — why
- SOM confidence: [High/Medium/Low] — why
**5. Key assumptions log** — A single list of every assumption used in the model, so the user can review and challenge them.
---
## CONTEXT FILE FOR NEXT STEP
After completing the above, create a downloadable file called `04-tam-mapping.md` structured as follows:
---
# TAM Mapping Summary
## Headline Numbers
- TAM: $[X] (range: $[low]–$[high])
- SAM: $[X]
- SOM (current trajectory): $[X]
- SOM (growth scenario): $[X]
## Methodology
[2–3 sentences on approach: top-down, bottom-up, or both. Note primary sources.]
## Segment Prioritization
[The segment table from the main output]
## Key Assumptions
[Bullet list of the most impactful assumptions — the ones that, if wrong, would change the numbers significantly]
## Confidence & Gaps
[Which numbers are solid vs. which are rough estimates. What data would improve accuracy.]
---
Keep this file under 500 words.
Tell the user: _"Download the context file below. When you're ready for Step 5 (ICP Validation & Positioning), start a new chat, upload all four context files, and paste in the Step 5 prompt."_