# Bottom-up SaaS market sizing worksheet > Estimate a defined market from eligible accounts and plausible spending rather than applying an arbitrary share to a broad industry total. Use the editable worksheet, example and review steps to turn it into a working document. Source: https://saas-marketing.net/templates/saas-market-sizing-model/ Topic: SaaS Market and Industry Data Type: template Published: 2026-09-17 Last updated: 2026-09-17 Publisher: SaaS Marketing (saas-marketing.net) License: CC BY 4.0. Quote or republish with attribution and a link to https://saas-marketing.net/templates/saas-market-sizing-model/ ## Short answer Bottom-up SaaS market sizing worksheet helps a SaaS team estimate a defined market from eligible accounts and plausible spending rather than applying an arbitrary share to a broad industry total. The fields below define the required decisions and evidence. Download a CSV working copy, assign owners and replace the illustrative example with your own approved information. ## Key takeaways - Estimate a defined market from eligible accounts and plausible spending rather than applying an arbitrary share to a broad industry total. - Do not call the theoretical market a sales forecast. Distribution capacity and competition require separate analysis. - Every field needs a useful answer, supporting evidence or an explicit unresolved question. - The download is an editable CSV file that opens in spreadsheet applications. --- Estimate a defined market from eligible accounts and plausible spending rather than applying an arbitrary share to a broad industry total. This worksheet supports the broader [saas market plan](/saas-market/). ## The working template | Field | What to enter | Your answer | Owner | | --- | --- | --- | --- | | Market boundary | Define customer, job, geography and period. | | | | Account source | Record where the count comes from. | | | | Eligibility | Document inclusion and exclusion rules. | | | | Account count | Estimate eligible businesses. | | | | Annual spend | State the comparable spending assumption. | | | | Serviceability | Remove accounts the offer cannot serve. | | | | Scenarios | Vary count and spend independently. | | | | Evidence log | Record source dates and limitations. | | | ## A worked example A model with 8,000 eligible firms and $4,000 annual spend implies a $32 million theoretical market before serviceability and obtainable-share constraints. The example is illustrative. It does not describe a measured customer result or create a promise about your own outcomes. Use it to understand the level of specificity the document needs. ## How to complete the worksheet 1. Choose one project, account segment or decision. A document that attempts to cover the whole company usually hides important differences. 2. Gather the evidence required by the fields above. Use approved customer research, current product information and the relevant business records. 3. Draft the answers with the person responsible for doing the work. Keep unresolved questions visible and assign a next action to each one. 4. Review the document with the people who depend on it. Confirm scope, responsibilities and any constraints before treating it as an operating agreement. 5. Save the version and review date. Update it when the underlying offer, process or customer evidence changes. ## Review before sharing Do not call the theoretical market a sales forecast. Distribution capacity and competition require separate analysis. A useful working document makes disagreements visible while there is still time to resolve them. Ask a colleague to explain the intended decision from the filled-in version without additional narration. If they cannot identify the next step or the evidence behind it, revise the relevant field. Remove confidential customer details from any public copy. Keep names, prices and results only when you have permission and can explain their context. An empty evidence field is a signal to investigate, not an invitation to supply a plausible-sounding number. ## Continue the work - [Global SaaS Market Size](/guides/global-saas-market-size/) - [SaaS Market Growth Rate](/guides/saas-market-growth-rate/) - [SaaS Industry Growth](/guides/saas-industry-growth/) - [B2B SaaS Market Size](/guides/b2b-saas-market-size/) - [The B2B SaaS Industry](/guides/b2b-saas-industry-overview/) Find more [templates](/templates/) and [checklists](/checklists/) for adjacent tasks. {/* expanded-practice-2026-09 */} ## Apply bottom-up saas market sizing worksheet in a working review Make a copy of the working file and complete one representative row before filling the entire document. Replace example values with evidence from the actual project. Add an owner and a review condition where the template calls for a decision. A blank marked unknown is more useful than an invented number that makes the file look finished. For this topic, involve the research owner and the person using the estimate for a decision and work from source method, market boundary and assumption table. The relevant unit is a clearly defined population, period and value measure. State the question the review should resolve before choosing a chart, an asset or a tool. If participants disagree about the unit or scope, resolve that disagreement before combining their evidence. ### Evidence to prepare Read the original definition before combining figures. Publication date, collection period and forecast horizon answer different questions. A market estimate can be useful without being directly comparable to another publisher’s number. | Review field | What to record | | --- | --- | | Topic | Bottom-up SaaS market sizing worksheet | | Decision | The specific action this explanation should help you choose | | Working evidence | source method, market boundary and assumption table | | Unit and scope | a clearly defined population, period and value measure | | Responsible people | research owner and the person using the estimate for a decision | | Remaining uncertainty | The missing fact that could change the decision | ### Two situations that can change the interpretation #### When TAM has no eligible-account rule Not every company in an industry needs or can adopt a particular operational workflow. Use this check: Define the customer workflow, geography, supported requirements and exclusion criteria. A large addressable market is not evidence of obtainable demand. The [focused diagnostic guide](/guides/tam-model-has-no-eligible-account-definition/) provides the correction process and a working evidence sheet. #### When a market estimate mixes unlike measures A software-only estimate and a software-plus-services estimate can both be reasonable while answering different questions. Use this check: Read each source's market boundary, unit, period and included products. Do not average conflicting definitions to create a falsely precise number. The [focused diagnostic guide](/guides/market-size-estimate-mixes-revenue-and-spend/) provides the correction process and a working evidence sheet. ### Record the decision and the limit A software-revenue estimate and a broader customer-spending estimate may both be credible within their own definitions. Averaging them does not create a better answer. Explain the boundary and choose the measure that matches the decision being made. Keep the conclusion beside the evidence that supports it. Record what the team will do, who owns the next action and which event or date will trigger a review. If the underlying definition, audience or product behavior changes, revisit the conclusion rather than assuming the old result still applies. A clear limit is useful information; it tells the next reader where additional investigation is required. Use the [complete topic collection](/topics/saas-market/) for related methods and the [category field guides](/industries/) when the product's buying situation or implementation requirements change how the method should be applied. ## Frequently asked questions ### What format is the downloadable template? The working copy is a CSV file. Open it in your spreadsheet application, add owners and dates, and keep a separate copy of the original for reference. ### How should I fill in this template? Estimate a defined market from eligible accounts and plausible spending rather than applying an arbitrary share to a broad industry total. Start with one real project so that the decisions remain specific. ### What mistake should I avoid? Do not call the theoretical market a sales forecast. Distribution capacity and competition require separate analysis. ### Do I need to complete every field before starting? Identify the fields that change the decision or block safe execution. Mark unknowns with an owner and a review date rather than inventing an answer.