Short answer
TAM, SAM and SOM are three nested measures of market size. TAM (total addressable market) is the annual revenue available if every possible customer bought from you. SAM (serviceable addressable market) is the part of TAM your product, price and reach can serve today. SOM (serviceable obtainable market) is the share of SAM you can realistically win in a set period. Calculate each one as the number of customers times annual revenue per customer.
- TAM is the ceiling, SAM is what you can serve today, SOM is what you can win in a set period.
- Each one is customers × annual revenue per customer; what changes is which customers you count.
- Count firms, not locations, when you price per company: Census Bureau SUSB data counts both.
- Derive SOM from sales capacity, then check the share it implies. Never start from "we'll get 1%".
On this page
This page is for founders writing a pitch deck, product and marketing leaders choosing segments, and sales leaders planning headcount. It defines the three numbers, gives the formulas, and works through a full example using real US Census Bureau counts, so you can see where each figure comes from.
What TAM, SAM and SOM mean
The three measures are nested: SOM sits inside SAM, which sits inside TAM. Each answers a different question.
| Measure | Stands for | Counts | Question it answers |
|---|---|---|---|
| TAM | Total addressable market | Every customer who could use this kind of product, at 100% market share | How big could this ever get? |
| SAM | Serviceable addressable market | The customers your product, price, geography and channels can serve today | Where can we compete now? |
| SOM | Serviceable obtainable market | The customers you can realistically win in a set period, given competition and capacity | What revenue should we plan for? |
All three are usually stated as annual revenue, not as customer counts. Say which year the figures describe and which customers are in each layer, or the numbers can't be checked.
The formulas
Each layer uses the same formula with a narrower count of customers:
- TAM = all potential customers × annual revenue per customer
- SAM = customers in the segments you can serve today × annual revenue per customer
- SOM = customers you can win in the period × annual revenue per customer
Where revenue per customer varies by size, calculate each size band separately and add them up. There are two ways to get the inputs:
| Method | How it works | Strength | Weakness |
|---|---|---|---|
| Top-down | Start from an analyst's market estimate and take a share of it | Fast | Analyst categories rarely match your product, and the share is usually a guess |
| Bottom-up | Count the customers who fit, multiply by your actual price | Every input can be checked | Takes longer, and needs a reliable count |
Bottom-up is the one to trust. Use a top-down figure only as a sanity check.
Worked example: a legal tech startup, with Census counts
Illustrative example. The company and its prices are invented; the firm counts are real.
Briefline (briefline.example) sells matter intake software to US law firms and prices per firm per year. The US Census Bureau's Statistics of US Businesses (SUSB) counts 156,583 law firms with paid employees in 2022 (NAICS 541110, Offices of Lawyers), split by the firm's total headcount. Briefline's prices are its own.
| Firm size (employees) | Firms (SUSB 2022) | Briefline price per year | Revenue if all bought |
|---|---|---|---|
| Fewer than 5 | 116,668 | $2,400 | $280.0M |
| 5 to 19 | 32,519 | $7,200 | $234.1M |
| 20 to 99 | 6,245 | $18,000 | $112.4M |
| 100 or more | 1,151 | $60,000 | $69.1M |
| All firms | 156,583 | $695.6M |
TAM: about $696M a year. That's every US law firm with employees buying at Briefline's price.
SAM: about $347M a year. Briefline is built for firms with 5 to 99 staff. Very small firms rarely pay for intake software, and firms of 100 or more need security reviews and integrations Briefline doesn't have yet. That leaves 38,764 firms: $234.1M + $112.4M = $346.5M.
SOM: about $2.8M a year by year three. Work it out from capacity, not from a percentage. Briefline plans two account executives, each closing four firms a month on average across three years: 2 × 4 × 36 = 288, call it 300 firms. If 240 are in the 5 to 19 band and 60 in the 20 to 99 band, that's 240 × $7,200 + 60 × $18,000 = $1.73M + $1.08M = $2.81M.
Check the share. $2.81M is 0.8% of SAM, and 300 firms is 0.8% of the 38,764 firms in it. A share under 1% after three years is believable for a new entrant. If the capacity maths had produced 15%, that would be the signal to recheck the win rate, not to celebrate.
One detail matters here. SUSB counts 166,972 law office establishments (locations) but only 156,583 firms, because some firms run several offices. Briefline prices per firm, so it counts firms. If you price per location or per seat, count locations or people instead.
Which number to use when
| You're deciding | Use | Why |
|---|---|---|
| Whether the opportunity is worth a company or a fundraise | TAM | It shows the ceiling and whether there's room to grow |
| Which segment to build for and sell into first | SAM | It shows the revenue your current product can reach |
| Next year's revenue plan, hiring and quotas | SOM | It's tied to capacity you can actually fund |
| Whether to expand into a new segment or country | SAM, recalculated for that segment | Expansion moves customers from TAM into SAM |
Common mistakes
- The 1% shortcut. "If we get just 1% of a $10B market" skips every question that matters. Derive SOM from how many deals your team can close.
- Counting people who'd never pay. A market of "all businesses" is not a TAM. Count the companies that have the problem.
- Mixing units. Counting locations but pricing per company, or mixing years from different sources, quietly inflates the result.
- A SAM that's really a TAM. If your SAM includes segments your product can't serve today, it isn't serviceable.
- Never updating it. Recalculate SAM when you add a product tier, a region or an integration.
Self-check before you present it
- Every customer count has a named source and a year.
- The price per customer is your real or planned price, by size band where it varies.
- You can say in one sentence who is in SAM and who is left out, and why.
- SOM comes from sales capacity and win rates, and the share it implies looks plausible.
- Someone else could rebuild the numbers from your table.
Once SAM is defined, the next job is turning it into named accounts. Bebop Insights supplies firmographic, technographic and signal data by API or bulk file, so you can count and pull the companies in each segment. The firmographics page explains the company attributes you'll filter on, and the ideal customer profile guide helps you choose the segment.
Next step: turn your SAM into a working list with the guide to building a prospect list.
Sources
- 2022 SUSB Annual Data Tables by Establishment Industry (US and states, NAICS detailed employment sizes), US Census Bureau, accessed 26 October 2026
- Statistics of U.S. Businesses: Methodology, US Census Bureau, accessed 26 October 2026
Written by the Bebop team at Blackpearl Group. Last updated .
Questions people ask
What is the difference between TAM, SAM and SOM?
TAM (total addressable market) is the revenue available if every possible customer bought your type of product. SAM (serviceable addressable market) is the part of that you can serve today with your current product, price, geography and channels. SOM (serviceable obtainable market) is the part of SAM you can realistically win in a set period, given competition and sales capacity. Each layer sits inside the one before it.
How do you calculate TAM?
Multiply the number of potential customers by the annual revenue you'd earn from each. Where price varies by customer size, calculate each size band separately and add them together. The most reliable customer counts come from government data, such as the US Census Bureau's County Business Patterns and Statistics of US Businesses, or from a company database filtered to the businesses that have the problem you solve.
What is a good SOM percentage?
There's no correct percentage, and starting from one is the most common mistake. Work out SOM from sales capacity instead: how many reps you'll have, how many deals each can close and your expected win rate. Then check the share of SAM it implies. A new entrant reaching under a few percent of SAM in its first few years is usually believable; double digits needs strong evidence.
Is SAM serviceable available market or serviceable addressable market?
Both names are in common use and mean the same thing: the portion of the total market your current product and go-to-market can actually serve. Pick one, define it on the slide, and stay consistent. What matters more than the name is stating exactly which customers are included and which are excluded, so anyone reviewing the number can check it.
Should TAM be top-down or bottom-up?
Bottom-up wherever you can. Counting the customers who fit and multiplying by your real price gives a number anyone can check. Top-down estimates start from an analyst's market figure, whose category rarely matches your product, and then apply an assumed share. They're useful as a sanity check: if your bottom-up TAM is far above the analyst figure, look for double counting.