1. Start with the economic unit of demand Skip the generic “market for X is $Ybn.” Define the smallest repeatable unit that creates cash for you:

• The buyer: who initiates, who approves, who blocks.
• The job: the specific use case that triggers spend and the frequency it occurs.
• The receipt: how value is packaged and billed (per seat, per site, per transaction, per project, subscription).

Remember in B2B your respondent is human—personal priorities and heuristics shape business choices. Treat values and trade‑offs (risk, status, convenience) as real drivers of willingness to pay, not afterthoughts .

2. Build three lenses of market size you can triangulate

A. Macro TAM with comparability guards

• Define the total relevant population (accounts or end users) and plausible ARPU for your job-to-be-done.
• If you cross geographies, align definitions, time periods, and coding so country data is truly comparable; plan for “equivalences” up front or you’ll rework the whole model later .

B. Usage TAM from the ground up

• Estimate total “events” that create spend. When a founder couldn’t get formal data on coffee demand, she asked suppliers how many cups local sandwich bars sold per day and per week, then backed into her sales potential—a classic bottom‑up move when official data is thin .
• For your niche, pick a proxy you can count: incidents, transactions, assets under management, machines in field, service calls, compliance checks. Multiply by achievable wallet share per event.

C. Reachable SAM inside your real channels

• Filter the above by your go‑to‑market reach in the next 12–24 months: channel footprint, list quality, procurement constraints, and segment fit.
• Use pragmatic segmentation to refine this. In SMEs, for instance, decision‑maker “types” differ in how they process offers and advice; one study isolated four “I’s” (Independence, Involvement, Identification, Intensity) and five segments that predicted response patterns with high accuracy—a simple, behaviorally grounded way to size the reachable slice you can actually move first . Combining segmentation diagnostics with other topics is common and helps tailor execution to the niche you’re truly addressing .

Cool insight: TAM answers “how big.” Your SAM answers “how many I can talk to.” Your cash plan answers “how many I can close and service.”

3. Price from willingness, not wishfulness

• Rapid WTP checks beat debates. One startup validated price acceptance with a single closed question—“How much would you pay for immediate answers?”—and found participants were prepared to pay. That simple distribution gave them a viable initial price band and region focus to target early adopters with the highest propensity to pay .
• Expect role‑based differences in what buyers value: some optimize for quality and reliability over price, others the inverse. “Why do customers buy?” is not rhetorical—it’s the input that determines where you can credibly command margin in your niche .

4. Translate market into a capacity‑bound revenue ramp Model monthly movement from first touch to cash in a way that reflects your actual throughput:

• Top‑of‑funnel reality: leads you can create per channel, per month.
• Conversion stack: MQL→SQL→closed won by segment, tied to your specific offer and price point.
• Time to live: the lag between booking and value delivery (implementation, data migration, training).
• Time to cash: billing schedule and payment terms.

Two practical tips:

• Use ranges where precision is false. Asking and planning with “approximately how many” beats pretending to know “exactly how many” in early B2B motions; ranges reduce respondent friction in discovery and help you build credible Low/Base/High scenarios for the model .
• Keep scales and categories consistent so your analysis doesn’t drown in harmonization work later (a subtle but frequent cause of planning drift) .

5. Convert revenue into cash‑flow targets you can manage to Set monthly cash‑flow targets that reflect:

• Bookings-to-billings lag: subscriptions, milestones, or per‑use events recognize revenue differently from when cash lands.
• Working capital drag: inventory or staffing hired ahead of revenue, and AR collection time.
• Churn and expansion: early churn mathematically dominates lifetime value; don’t bury it. Model cohort cash over a 12‑month horizon, then a 24‑month horizon.

Then overlay capacity:

• Sales capacity: ramp time to full quota, win rates by segment, and the hiring/staggering plan.
• Delivery capacity: the implementation and support ceiling that gates recognized revenue and renewals.

Cool insight: SOM is not a percentage you pick—it’s the product of your monthly capacity and the niche’s conversion physics. If your delivery lane can onboard 15 logos per month, that is your SOM until you unlock the next constraint.

6. Stress‑test with the three deltas that kill plans

• Price −10%: what happens to win rate and cash runway?
• Slip +30 days: add a month to go‑live or payment for half your pipeline—does your working capital hold?
• Hire −1: if one rep or engineer arrives 60 days late, how many months do you lose on target?

Action‑plan the gaps with the same discipline you’d apply to any critical project—define activities, sequence, and trade‑offs across result, time, and cost. Planning techniques that force you to reveal omitted steps and critical paths help convert sizing into shipping and billing .

7. Put the numbers on one page—and decide Your decision‑ready brief should include:

• The unit of demand and your price band by segment.
• TAM/SAM and the first‑year, capacity‑bound SOM.
• A 12‑month cash‑flow ramp (Low/Base/High) with explicit lags and assumptions.
• The two constraints that matter most (e.g., implementation throughput and procurement cycle time) and the one experiment that could change your slope fastest.

What this approach avoids

• Cross‑country apples‑to‑oranges: your TAM doesn’t quietly inflate because two countries defined the niche differently; you planned equivalences from the start .
• “Top‑down only” mirages: you ground truth with usage proxies and buyer research instead of slogans; even a single closed WTP question can validate a beachhead price region and regionally specific demand .
• Role‑blind pricing: you account for why customers buy—price vs quality, reliability, peace of mind—and align offers and CAC accordingly .

Final cool insight Your first realistic cash‑flow target is not “1% of TAM.” It’s the sum of:

• How many real demand events you can intercept in your chosen micro‑segment,
• At a price your early buyers already accept,
• At a pace your sales and delivery capacity can actually handle,
• Paid on a timetable your working capital can survive.

Do that, and you’ll have numbers you can commit to—and hit.