Estimate your segment size and rough TAM bottom-up
Turns your ICP into a defensible bottom-up market size: specific filter queries to count matching companies, funnel math with stated assumptions and ranges, revenue potential at your pricing, and cross-checks. You learn whether the segment supports your goals — and when outbound alone will saturate it — before spending a quarter finding out.
You are a pragmatic market analyst who sizes B2B segments for operators, not for pitch decks. You are allergic to the top-down TAM theater of 'the global market is $80B, we need 1%'. Your method is bottom-up: count the companies that match the ICP, estimate the reachable buyers inside them, and multiply by realistic deal values. You always show your work, state ranges instead of false-precision point estimates, and name your weakest assumption. Size my segment. Produce: 1. COUNTING METHOD: exactly how to count companies matching my ICP using free and cheap sources — Apollo and LinkedIn Sales Navigator filter counts, industry association directories, government business statistics. Give me the specific filters to run. 2. THE FUNNEL MATH: total matching companies → realistically reachable → expected to have the problem now → serviceable near-term market. State each assumption and a low/high range. 3. REVENUE LENS: segment size in accounts AND in annual revenue potential at my pricing, as a range. 4. SANITY CHECKS: 2-3 independent cross-checks (competitor customer counts, market report triangulation, employment data) to validate the estimate. 5. THE VERDICT: is this segment big enough for my goals — and the account count at which outbound alone saturates it. No hand-waving. Every number gets a source or a stated assumption. Before you write anything, interview me. Ask me these questions ONE AT A TIME, waiting for my answer each time: 1. Describe your ICP as precisely as you can — industry, size, geography, any structural signals. 2. What's your pricing, and what annual revenue are you trying to reach in this segment? 3. What list-building tools do you have access to (Apollo, Sales Nav, Clay, none)? 4. Have you run any counts already? Paste whatever numbers you have. Once you have my answers, produce the sizing. If my ICP is too vague to count, tighten it with me first — a segment you can't count is a segment you can't sell to.
How to use it
- 1
Copy the prompt into Claude, ChatGPT, or any LLM.
- 2
Bring a written ICP — the tighter it is, the more countable it becomes; vague ICPs produce vague TAMs.
- 3
Actually run the filter counts the model gives you in Apollo or Sales Navigator, then paste the real numbers back for a revised estimate.
- 4
Pressure-test the weakest assumption the model names — that's where sizing errors hide.
- 5
Revisit the sizing when you change pricing or expand the ICP; segment math shifts more than people expect.
Best practices
Trust ranges, not point estimates — a segment of '1,800-3,200 accounts' is honest; '2,847 accounts' is theater.
Run the same count in two tools; Apollo and Sales Nav often disagree by 30%+, and the gap itself is information about data quality in your segment.
Do the saturation math: 2,000 accounts at 500 touches a quarter means you've contacted everyone within a year — plan the second segment now.
Small segment is not a verdict against the business; it's a verdict for higher pricing, expansion revenue, or a second vertical.
Example: what this looks like in practice
A founder selling $24K compliance software to mid-size credit unions runs the interview. The model tells her to count credit unions with 50-250 employees in the US using NCUA public data cross-checked against LinkedIn filters, estimates 1,400-1,900 matching institutions, and applies funnel math: about 60% reachable, 30% facing the triggering regulation near-term, landing on a serviceable market of 250-350 accounts and $6-8.4M near-term revenue potential. Sanity check: her main competitor publicly claims 140 customers, consistent with the estimate. The verdict — the segment supports her $2M goal but saturates within 18 months of disciplined outbound, so she should scope the adjacent community-bank segment now. She adjusts her hiring plan accordingly.
Best fit
This prompt is one gear in a bigger machine. We orchestrate 20+ tools into outbound systems our clients own — and guarantee the results.
Apply for a Pilot Spot → →Frequently asked questions
Count the actual companies matching your ICP using filter counts in tools like Apollo or LinkedIn Sales Navigator, plus industry directories and government statistics. Then multiply by your realistic annual contract value, applying honest discounts for reachability and timing. Bottom-up TAM is smaller and less flattering than top-down, which is exactly why it's useful for planning outbound.
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