A slide stating that the “market is worth 4 billion zł” gets through the board only once – until someone asks where that figure came from and what exactly was included in it. The question how to calculate TAM SAM SOM is not about a formula, but about the data chain: which sources, which assumptions, which filters, and what logic is used to move from the theoretical market to the share a company can realistically capture. Below is an overview of the research approach that makes it possible to document this figure rather than merely present it.
What is market sizing and why does the question “how to calculate TAM SAM SOM” come too late?
Market sizing is the process of estimating the value or volume of demand in a defined category, within a defined area, and over a defined period. Three levels of estimation clarify concepts that are often confused in practice:
- TAM (Total Addressable Market) – the total value or volume of the market for a given category, assuming the company fully covers the defined market. It represents the maximum potential within the adopted definition of category, geography, and period.
- SAM (Serviceable Available Market, also often referred to as Serviceable Addressable Market) – the portion of TAM available to a company given its product or service and the adopted boundaries, such as geography, customer segment, sales model, channel, or legal or technical requirements.
- SOM (Serviceable Obtainable Market) – the portion of SAM that an organization can realistically capture within a given time horizon, taking into account its resources, channel access, competition, and speed of market entry.
The order of definition is critical, not the order of calculation. TAM without a defined unit of analysis (who the buyer is, what the product is, what the purchase cycle looks like) produces a figure that cannot be broken down into its components. This is why the question how to calculate TAM SAM SOM usually comes too late – when the presentation is already complete and the assumptions have been made implicitly.
Market sizing serves three functions in a research project: it establishes the denominator for calculating market shares, provides a basis for forecasting demand in subsequent periods, and enables segments to be compared using the same unit of measurement. Without a common denominator, discussions of market potential become an exchange of opinions.
How to calculate TAM, SAM, and SOM? Methods, sources, and sequence of steps
In research practice, three approaches are used, most often in parallel, so that their results can serve as mutual checks.
Top-down approach
The starting point is an aggregated market value from secondary data (public statistics, industry reporting, customs data, registers, and reports from chambers of commerce). Successive narrowing filters are then applied: country, region, customer segment, product type, and channel. The advantage is speed and reliance on an external source. The limitation is that statistical classifications rarely align with the boundaries of a business category, so each filter introduces additional uncertainty.
Bottom-up approach
The market is calculated as the product of: the number of demand units × purchase frequency × unit value. In B2C, the unit is a household or consumer; in B2B, it is a company with a specific profile (PKD, employment size, installed equipment base, existing IT system). Data on penetration, frequency, and basket value can be collected through quantitative research on a sample selected from the population defined in the sampling frame. This approach provides the greatest control over assumptions because each component of the calculation has its own source, and measurement uncertainty can be estimated for parameters derived from sample-based research.
Value and substitution approach
Where a category is new and has no sales history, the market is estimated based on the expenditure it replaces: how much an organization currently spends to solve the same problem in another way. Data are collected through in-depth interviews (IDIs) with purchasing decision-makers and studies of stated willingness to pay. The result should be treated as a hypothesis about market potential, not as a sales forecast.
The sequence of work in a market sizing project usually looks as follows – each step ends with a documented assumption that can be revisited:
- Definition of the category and unit of analysis. What is included, what is excluded, and in which unit market size is measured (value, volume, number of users, number of contracts).
- Desk research and source audit. An inventory of secondary data, including an assessment of its currency, scope, and the definitions used by the source.
- Identification of data gaps. Identifying parameters that cannot be reconstructed from secondary sources – these determine the scope of primary research.
- Quantitative research. CATI, CAWI, or mixed-mode research on a sample selected for the purpose of the study; measurement of penetration, frequency, basket value, and channel structure.
- Interviews with market participants. IDIs with distributors, installers, and wholesalers are used to calibrate and interpret the data, as they may provide information on volume flows in the portion of the market they serve.
- Triangulation. Comparing top-down and bottom-up results; a material discrepancy relative to the adopted threshold requires the definitions, sources, and assumptions in both approaches to be reviewed.
- Narrowing down to SAM. Applying filters resulting from the fit of the offering: geography, regulations, certification requirements, and channel availability.
- Calculation of SOM. Applying the organization’s resource constraints, competitive conditions, and market entry plan to SAM, while specifying the key limiting factors.
- Sensitivity analysis. Three outcome scenarios indicating which variable has the greatest impact on the result.
TAM is useful as a description of the maximum potential within the adopted market definition, but it does not in itself determine a company’s possible sales. SOM links potential to a realistic action plan, resource constraints, and competition, and should therefore be compared with sales performance and resource utilization.
A practical example of a bottom-up calculation for a B2B service offering: the population of companies with a specific type of equipment (business register plus data on installed equipment from the research) × the share of companies outsourcing service work (declarative measurement in CATI) × the number of interventions per year (behavioral measurement, asking about the previous 12 months) × the average order value (measured using ranges rather than an open-ended question). Each of the four factors should have a separate source and description of uncertainty, so that the result can be defended component by component.
Which errors most often undermine market size estimates?
Most estimates challenged by the board have one of several recurring flaws. The following are the most common in market sizing projects:
- Category defined too broadly. Including in TAM everyone who “could” buy, rather than clearly defining the buyers and the need covered by the category. The result is a large but non-operational figure – it is not possible to derive SAM from it reliably.
- Double counting in the distribution chain. Adding together manufacturers’ and wholesalers’ sales. The solution is to make an unambiguous decision about the level of the chain at which value is measured and consistently use prices from that level.
- Mixing prices. Some data are at manufacturer prices, while others are at tax-inclusive retail prices. The discrepancy can be greater than the difference between scenarios.
- SOM as a percentage of TAM. The classic shortcut: “we will capture 1% of the market.” A share adopted arbitrarily is not a calculation result. SOM should be based on justified assumptions about resources, channels, competition, and the pace of customer acquisition.
- Purchase intention treated as demand. The percentage of respondents declaring interest in purchase is a measure of attitude, not volume. For market sizing, it is worth using questions about past behavior and actual expenditure, while comparing declarations with sales data or market test results.
- The market as a point, not a range. A single figure without a range and without identifying the critical variable cannot be discussed – it can only be accepted or rejected.
- Outdated secondary data without a note. Using a source without indicating the reference year and methodological changes made by the institution collecting the data.
An alternative or supplement to the declarative approach is methods based on existing data: analysis of transaction data, retail panel data, customs and import data, and, in digital categories, analysis of search volumes as an indicator of interest in the category. None of these methods measures the market directly, but each can provide an independent checkpoint. The credibility of an estimate increases not only with the number of interviews, but above all with the quality and independence of sources that lead to similar results.
What should be included in the documentation of an estimate presented to the board?
A figure can be defended when the method by which it was developed is presented alongside it. The minimum documentation should include several elements whose absence is the most common reason an analysis is sent back for revision:
- Category definition with a list of exclusions – what was deliberately excluded from TAM and why.
- Unit and level of measurement – value or volume, net or gross prices, manufacturer or retail level, reference year.
- Source table – for each calculation component: source, date, method of collection (secondary data, CATI, CAWI, IDI), and, for sample-based research, also sample size and sampling method.
- Assumptions sheet – each conversion factor from TAM to SAM and from SAM to SOM documented separately, with a rationale.
- Key SOM constraints – identification of factors that limit the acquisition or servicing of demand (capacity, distribution, service, sales team, competition).
- Sensitivity analysis – three result scenarios and information on which variable has the greatest impact on the outcome.
- Range of uncertainty – a range rather than a point estimate, together with a description of the method’s limitations.
This set changes the nature of the discussion: instead of disputing a number, the board discusses a specific assumption that can be changed and recalculated. This is the most practical answer to the question how to calculate TAM SAM SOM – calculate it so that every step can be reconstructed without the author of the spreadsheet.
Frequently asked questions
What is the difference between TAM, SAM, and SOM?
TAM measures the maximum potential of a defined market, SAM narrows it down to the share accessible to a company’s offering under a given business model, geography, and regulatory requirements, and SOM narrows it further to the share the company can realistically capture within a specified period. The practical difference lies in the assumptions: TAM describes the scale of the category, while SOM takes into account resources, channels, competition, and the sales plan. All three levels should be calculated using the same unit and for the same period; otherwise, they cannot be compared.
Where can data for estimating market size be obtained?
Secondary data include public statistics, business registers, customs and import data, financial statements of market participants, publications from industry chambers, and retail panel data. Gaps not covered by these sources (penetration, purchase frequency, basket structure, and the share of outsourced purchases) can be filled through primary research: CATI or CAWI on a sample selected for the purpose of the study, plus IDIs with intermediaries familiar with part of the channel. Each source requires its category definition to be checked, as statistical classifications rarely correspond to the boundaries of a business category.
How can you verify whether a market estimate is credible?
The basic test is triangulation: calculating the market independently using top-down and bottom-up methods and comparing the results – convergence within a similar range is a stronger argument than the apparent precision of a single calculation. The second test is reconstruction: can a third party, given the assumptions sheet and source table, reproduce the result without contacting the author? The third is sensitivity analysis – if changing a single assumption by several percentage points changes the result many times over, the estimate requires additional verification of that specific variable.
Ask about market sizing for your category
Hume’s Institute designs market sizing research that combines desk research, quantitative measurement, and interviews with channel participants, so that TAM, SAM, and SOM can be reconstructed component by component. Contact us to discuss the scope of data and methods needed for your category.