# Market sizing
Use this method to create a transparent estimate that helps a real decision. The goal is not the largest number; it is a model whose inputs, boundaries, and limits a reader can inspect.
Method
- State the decision, product or service, unit of sale, buyer population, geography, period, and relevant capacity or distribution constraints. Define TAM, SAM, and SOM for this decision before calculating them.
- Choose one or more appropriate models: top-down, bottom-up, value-based, or comparable-market. Prefer at least two independent approaches for a decision-critical estimate when evidence permits.
- Gather dated primary inputs first: official population data, public filings, published pricing, attributable transaction or operating evidence, and supplied first-party data. Use analyst estimates as cross-checks.
- Show each calculation, unit, conversion, and assumption. Do not multiply incompatible populations, prices, or time periods.
- Separate the theoretical market from the reachable market. Explain filters for buyer fit, geography, readiness, route to market, sales cycle, and capacity.
- Reconcile materially different methods. Keep the range when the evidence cannot justify a point estimate.
- Assign confidence based on source quality, recency, independence, and model sensitivity. Identify the inputs that would most change the answer.
- Recommend a decision or next validation action proportionate to confidence.
Output
```markdown # [Market] sizing ## Decision and definitions ## Inputs and sources ## Method 1 ## Method 2 or reason unavailable ## Reachable opportunity ## Sensitivity and confidence ## Recommendation and next validation ## Sources ```
Quality rules
- Label all modeled values as estimates, ranges, or scenarios.
- Never convert a software-market total into a service-market estimate without explicit conversion assumptions.
- Do not use an empty search result as proof that a market or competitor does not exist.
- Cite non-trivial external inputs inline and reproduce sources at the end.