TAM, SAM, SOM: Meaning and How to Calculate
TAM, SAM, and SOM describe three levels of market opportunity: total addressable market, serviceable addressable market, and serviceable obtainable market. In Amazon Ads’ definitions, TAM is the full revenue opportunity, SAM is the portion a business can serve, and SOM is the portion it can realistically capture.
What is the difference between TAM, SAM, and SOM?
| Measure | Full name | What it measures | Main question |
|---|---|---|---|
| TAM | Total addressable market | Revenue potential across the entire defined market | How large is the opportunity? |
| SAM | Serviceable addressable market | Revenue potential within the serviceable portion of TAM | Which part can the business serve? |
| SOM | Serviceable obtainable market | Revenue realistically attainable within SAM | Which part can the business win? |
SAM is also called serviceable available market, as in the UK government’s market-sizing guidance. Both names refer to the serviceable portion of TAM.
The relationship is SOM ⊆ SAM ⊆ TAM: obtainable customers sit within serviceable customers, who sit within the total defined market. For a revenue comparison, use the same product definition, currency, pricing basis, and period across all three figures. Keep customer counts alongside revenue values so the calculation remains visible.
How to calculate TAM, SAM, and SOM
Define the product, customer, and period
Begin with the product or service being sized, the customer group, the geographic boundary, and the revenue period. The U.S. Small Business Administration’s market-research guidance separates demand, market size, location, market saturation, and pricing into distinct research questions. Answering those questions establishes what the calculation covers.
Record the inputs before calculating:
- The product or service and the need it addresses.
- The eligible customer group and geographic scope.
- The unit being counted: people, households, businesses, locations, or purchases.
- Revenue per unit and the period it represents.
- The source and reference year for each input.
Match the population count to the buying unit. The Census Bureau’s business glossary distinguishes an establishment, a physical business location, from an enterprise, which can contain multiple establishments. Use a location count with revenue per location and an enterprise count with revenue per enterprise. Mixing the two units changes the result without changing the underlying opportunity.
Calculate TAM: the total opportunity
The basic TAM formula multiplies potential customers by average revenue per customer:
TAM = total eligible customers × average annual revenue per customer
This produces an annual revenue estimate. Define eligibility by the product and its potential buyers. Use annual revenue per customer consistently; a purchase price needs purchase frequency before it becomes an annual revenue input.
For a segmented calculation, use segment customers × segment annual revenue per customer for each non-overlapping segment, then add the results. Keep the segment counts and prices visible rather than applying one price to every buyer.
Calculate SAM: the serviceable opportunity
Filter the TAM population to the customers the offer can serve. The UK guidance identifies geography, customer type, and regulation as serviceability constraints.
SAM = serviceable customers × average annual revenue per serviceable customer
State each inclusion rule and apply the rules to the same underlying population. Geography and customer type can overlap, so adding their separate counts can count the same buyer twice. Calculate the intersection of the serviceability conditions instead.
Use the pricing appropriate to the remaining customers. A change in the customer mix can change average revenue per customer; a customer-count percentage and a revenue percentage need not be equal.
Calculate SOM: the obtainable opportunity
SOM estimates attainable revenue or market share. Corporate Finance Institute’s SOM guide identifies reach, business capabilities, product demand, competition, historical performance, and external research as inputs.
SOM = SAM × achievable share of SAM revenue
The share must refer to revenue when SAM is measured in revenue. An equivalent customer-based calculation is obtainable customers × average annual revenue per obtainable customer, provided the customer and pricing assumptions match.
Specify the capture period. The UK investor-readiness guidance treats SOM as a target supported by strategy, resources, and traction over a stated horizon. Label the target date separately from the revenue period: annual revenue attainable by a future date differs from cumulative sales up to that date.
Support the obtainable-customer estimate with recorded sales results, channel reach, demand research, and delivery capacity. Document the assumptions still awaiting evidence. The SOM formula supplies the arithmetic; the supporting data supplies the reason to believe the share is attainable.
Top-down, bottom-up, and value-based market sizing
Corporate Finance Institute describes three approaches to estimating TAM: top-down analysis, bottom-up analysis, and value theory.
| Method | Starting point | Calculation approach | Input to substantiate |
|---|---|---|---|
| Top-down | A broader market or population estimate | Narrow it to the relevant product and customer segments | The market boundary and every filtering proportion |
| Bottom-up | Customer counts, pricing, and usage research | Build revenue from the relevant customer or purchase units | Eligible units, spending, and purchase frequency |
| Value-based | The value a product creates for customers | Estimate how much value can be reflected in pricing | Customer value and willingness to pay |
Bottom-up sizing makes the customer count and revenue assumptions explicit. Top-down sizing supplies a broader comparison. Compare the two using matching definitions and investigate differences in product coverage, geography, or period before choosing a figure.
Value-based sizing requires a separate pricing assumption. Customer value and seller revenue are different quantities; enter the amount expected to be captured through pricing in the revenue model. Record research supporting that amount.
Where to find data for the calculation
For U.S. business counts, check what the statistical unit includes. The Census Bureau’s CBP glossary states that establishment counts represent locations with paid employees and that County Business Patterns excludes nonemployer businesses. It points to Statistics of U.S. Businesses for enterprise-level statistics. Choose the series that matches the buying unit and record its coverage limits.
For consumer markets, the Bureau of Labor Statistics’ Consumer Expenditure Surveys provide U.S. expenditure, income, and demographic data, with demographic and geographic tables. Use the relevant spending category and population group as inputs, with their reference year. Category spending supplies context for a product estimate; the model still needs a defined eligible population and revenue attributable to the offer.
For product demand and purchasing behavior, combine published statistics with direct research. The SBA explains that existing sources answer broad, quantifiable questions, while surveys, questionnaires, focus groups, and interviews can answer questions specific to potential customers. Record which findings support the buyer definition and which support pricing or expected adoption.
What makes a SOM estimate credible?
A small percentage alone provides little evidence of attainability. Corporate Finance Institute warns that even a small assumed share of a broad market can overestimate revenue. Evaluate the chosen share against the relevant product segment, competitors, reach, and performance data.
Report SOM as an estimate with a stated horizon and supporting assumptions. Use a range for uncertain inputs and calculate how those ranges affect the result. Keep measured customer counts, observed prices, and estimated adoption rates distinguishable in the model.
Before presenting the figures, check that:
- TAM and SAM use a defined product and customer population.
- Customer counts match the revenue unit, with overlaps removed.
- All revenue figures use the same currency and period.
- SAM filters describe documented serviceability boundaries.
- SOM has a target date and evidence for its obtainable share.
The UK guidance calls for market figures grounded in evidence and logically connected. Present each figure with its formula, input sources, reference dates, and assumptions so the total opportunity, serviceable opportunity, and attainable revenue can be assessed separately.