TAM, SAM and SOM Explained for First-Time Founders
If you’re working on a business idea, you may run into three acronyms: TAM (total addressable market), SAM (serviceable available market), and SOM (serviceable obtainable market). They show up in business plans and pitch decks, the slides founders show investors. Together they describe your market at three levels of zoom: everyone with the problem you solve, those you could serve, and those you could realistically win.
What TAM, SAM, and SOM mean
Picture them as three circles, each inside the last. Plans usually state each circle as money: what those customers would spend in a year. Say you want to offer online math tutoring for high school students.
Total addressable market (TAM)
This is everyone who has the problem your kind of product solves and would pay to solve it, as if you could reach them all and had no competitors. For the tutor, that’s every high school student, anywhere, whose family would pay for help with math.
Serviceable available market (SAM)
This is the part of that total you could actually serve, given your location, your language, the way you sell, and the version of the product you’ll really offer. For the tutor, that might be students who learn in your language, follow a curriculum you know, and live in time zones that fit your hours.
Serviceable obtainable market (SOM)
This is the share of the serviceable market you could realistically win in the time frame you’re planning for. It accounts for the other options people already have, how many of them you can reach, and how much work you can take on. For the tutor, it’s the families you can actually find, convince, and fit into your week.
Why each one matters, and when it doesn’t
TAM shows how much room there is. It tells you whether the need is widespread enough for the business to grow beyond its first customers. Investors often ask for it because they’re looking for businesses that could become very large.
SAM shows who you can actually serve. It makes you describe your customers and your reach specifically, which helps you decide where and how to sell. Adding delivery or selling online redraws it.
SOM is the one your plan stands on. Your sales forecast (your best estimate of what you’ll sell), how much to spend on supplies, and whether the business can pay you all depend on what you can actually win.
When don’t they matter much? If you aren’t raising money from investors, you may never be asked for a TAM, and a modest market can still support a good business. Early on, evidence that your first customers will pay matters more than a polished diagram. These estimates are a tool for thinking, not a test to pass before you begin.
How to estimate TAM, SAM, and SOM
Both methods below produce an estimate, never a fact.
Top-down: start big and narrow it
A top-down estimate starts with a published total for a whole category, from an industry report, a trade association, or government statistics, and narrows it with assumptions:
size of the whole category = roughly your TAM
TAM × share in the places you can serve × share that fits your offer = your SAM
SAM × share you could realistically win = your SOM
It’s quick and gives you a sense of scale. But the published category may not match what you sell, and the shares are often guesses. Multiplied together, guesses can drift far from reality without anyone noticing.
Bottom-up: start from real customers
A bottom-up estimate starts from customers you can picture, count, or reach, and builds upward:
number of customers × how often each buys in a year × typical price
Count everyone who has the problem and would pay to solve it for your TAM, those you could serve for your SAM, and those you could realistically win for your SOM. For your SOM, that count often needs its own formula:
people you can reach × share who are interested × share of those who actually buy
It takes more work, but you can check most inputs by observing, asking, or running a small test, which makes the result easier to trust.
If the two methods disagree sharply, find the assumption that changes the result most and test it. Either way, note where each assumption came from (something you saw, were told, or guessed) and show those sources when you present the estimate. Guesses are fine early on, as long as you know which ones they are.
Common mistakes when sizing a market
Starting from a huge headline market
It’s tempting to quote the size of a whole industry and say you only need a small slice. But that size says nothing about why anyone would choose you, and the slice may be picked because it sounds modest, not because anything supports it. Start from who would buy first, then work outward.
Confusing interest with demand
Compliments, likes, and “I’d definitely buy that” are interest. Evidence of demand is a commitment: a preorder, a deposit, or switching from what someone uses now. If you base the share who buy on what people said rather than what they did, your SOM will likely be too high. So ask what people currently do and spend.
Ignoring reach
A customer you can’t reach isn’t in your obtainable market, however well your offer fits them. For each group you count, ask how they would hear about you and what it would cost, in time or money, to get in front of them.
Example: TAM, SAM, and SOM for a local coffee cart
Say you’re thinking about a weekend coffee cart. Its TAM, everyone who buys coffee while out, is too broad to guide decisions. Its SAM is the coffee buyers who pass the spots you could use while you’d be open. Its SOM is the share of them who’d choose your cart, up to what you can serve. You can learn much of this by watching and asking:
- Where would you set up? A farmers market, a park entrance, and a sports field on game days each draw different people with different reasons to stop. Each spot may need permission or a permit, so check with the organizer or your local authority before counting on it.
- Who walks past? This is foot traffic. Stand where the cart would be, at the hours you’d be open, on more than one weekend. Count how many pass, and notice who is rushing or lingering and who already has a drink. Weather and events change what you see, so note them too.
- What else is nearby? A café across the street or another cart competes for the same customers. What would make someone choose you instead?
- How much can you serve? Capacity is how much you can make and hand over in the time you have. It sets a limit, however many people pass.
One way to estimate that limit:
drinks you can make in an hour × hours you’re open × days you operate
Expect to serve less than this: customers arrive in rushes, and a long line turns people away.
Your realistic sales are the smaller of two things: what passers-by will actually buy from you, and what you can serve.
Even rough observations can show which spot and hours look most promising. When you’re ready to estimate, the people who pass during your hours are the people you can reach in the bottom-up formula. Revise as you learn.
If you’d like somewhere to work through questions like these with your own idea, BizWizard introduces business concepts as they come up and helps you apply them to what you’re building. Read How It Works for an overview, or Request Access when you’re ready.