HomeCasa TAM, SAM and SOM market sizing without made-up data
Estimate your market size with a transparent bottom-up and top-down method, explicit assumptions and sources to verify instead of invented numbers. Designed for ChatGPT, Claude, Gemini and Perplexity. It includes 5 customizable variables and you can copy it for free in one click.
Advanced · Text · Pending editorial review
Prompt
Act as a strategy and market research analyst. Your priority is methodological transparency: I prefer a calculation with clearly flagged gaps to a made-up number.
Context:
- Product or service: {{product}}
- Target customer: {{customer}}
- Geography: {{geography}}
- Revenue model and price: {{pricing}}
- Data I already have: {{own_data}}
Deliverables:
1. Definitions applied to my case: what counts as TAM, SAM and SOM and what is excluded, with explicit criteria.
2. Bottom-up calculation: number of potential customers × adoption rate × average price × frequency. Show the formula and leave each variable as [DATA: what to look for and where], suggesting specific sources (Census Bureau, BLS, industry associations, public filings, trade reports).
3. Top-down calculation as a cross-check, using the same placeholder logic.
4. Assumptions table: assumption, provisional value, rationale, confidence level (high/medium/low) and how to validate it.
5. Three SOM scenarios (conservative, base, optimistic) over 3 years, explaining what would have to happen in each.
6. Sensitivity analysis: the 2-3 variables that move the result the most.
7. Validation checklist: interviews, surveys or demand tests to confirm the assumptions.
Constraints:
- Do not invent market figures, market shares or report names. If you know a public figure, give the source and year so I can check it; otherwise use [FILL IN].
- Always separate verified facts, estimates and assumptions.
- If information is missing to define the segment, ask me before calculating.
Format: numbered sections, visible formulas and tables.How to use it
Use Perplexity or your own research to fill each [DATA] slot with official sources, then paste the values back to recalculate. Keep the assumptions table: it is what investors will question most.
Usage example
Product: management app for language schools · Customer: schools with 50-500 students · Geography: United States · Price: 49 USD/month.
Sample output
1. Definitions applied
- TAM: every yoga and Pilates studio in the US and Canada that takes bookings, independent or chain.
- SAM: only independent studios with group classes and advance booking. General gyms and chains with in-house software are excluded.
- SOM: the share of the SAM you can realistically win in 3 years with your current sales capacity.
2. Bottom-up calculation
Annual SAM = number of independent studios × $39 × 12 months
| Variable | Value | Suggested source |
|---|---|---|
| Yoga and Pilates studios | [DATA: business counts by industry code] | Census Bureau County Business Patterns / Statistics Canada |
| % independent | [DATA: sample of directories and Google Maps] | Own research |
| Average price | $39/month | Own data |
4. Assumptions
| Assumption | Provisional value | Confidence | How to validate |
|---|---|---|---|
| Waitlist conversion | [FILL IN]% | Low | Pre-sale to the 120 studios |
| Monthly churn | [FILL IN]% | Low | Track the pilot cohort |
5. SOM scenarios (year 1)
- Conservative: only part of the waitlist converts → 120 × [conversion] × $39 × 12.
- Base: waitlist + organic acquisition in [FILL IN] cities…
Key facts
- Category
- Business & entrepreneurship · Market research
- Output type
- Text
- Level
- Advanced
- Designed for
- ChatGPT, Claude, Gemini and Perplexity
- Verified in
- Pending editorial verification
- Variables
- Product or service, Target customer, Geography, Revenue model and price and Data I have
- Language
- English
- Price
- Free, no sign-up
- Updated
- Nov 7, 2026
Frequently asked questions
What is the difference between TAM, SAM and SOM?
TAM is the entire possible market; SAM is the part your product and channels can actually reach; SOM is the share you can realistically capture in a given timeframe.
Why is bottom-up more reliable?
Because it builds on real customers, prices and adoption rates you can verify, while top-down relies on percentages from broad reports that are hard to justify.
What is this prompt for?
Estimate your market size with a transparent bottom-up and top-down method, explicit assumptions and sources to verify instead of invented numbers.
Which AI tools does it work with?
It is designed for ChatGPT, Claude, Gemini and Perplexity. We have not verified it in these tools yet, so results may vary between them.
How do I customize the prompt?
Click “Customize” and fill in the variables (Product or service, Target customer, Geography, Revenue model and price and Data I have). The text updates instantly and you can then copy it in one click. Values are stored only in your browser.
Do I need experience to use it?
It is advanced: it is meant for people with experience in the topic who can evaluate and adjust the result.
Is this prompt free?
Yes. Every HomeCasa Prompts prompt is free, with no sign-up or subscription. You can also use them in professional projects.
Can I trust the AI output?
Treat it as a high-quality draft: always check data, figures and important claims before publishing or making decisions.