Every pitch deck seems to include a market sizing slide with three concentric circles. The biggest says TAM, the middle says SAM, and the smallest says SOM. The numbers on them tend to be enormous, which is part of the problem. If you came here asking “what is SAM versus TAM,” here are the plain definitions first, followed by a more honest conversation about market sizing and how to use it without fooling yourself.
The definitions behind market sizing
A fuller walkthrough lives in our guide to sizing your market, but the short version follows.
TAM, total addressable market. The total revenue available if every possible customer bought your type of product. It’s the theoretical ceiling for the category.
SAM, serviceable addressable market. The portion of the TAM you can actually reach with your product, business model, geography and distribution. If you sell a tool for dentists in one country, the worldwide healthcare software market is not your SAM.
SOM, serviceable obtainable market. The slice of the SAM you can realistically win in a defined period, given competition, sales capacity and funding.
A quick example. Suppose you build scheduling software for independent yoga studios. TAM might be all yoga and fitness studios in the world multiplied by what they’d pay. SAM narrows to studios in countries you support, in your language, who don’t already use a chain-wide system. SOM is the number you can plausibly sign up over the next few years.
Two ways to approach market sizing
Top-down. Start with a total addressable market figure from an industry report that states a big number, then take a percentage. It’s fast and widely used, and it’s the one investors trust least. “If we get just one percent of a ten-billion market” is a famous cliché for a reason.
Bottom-up. Count real customers and multiply by price. How many studios exist? What would each pay per month? How many can one salesperson close per quarter? This is slower but much more credible, because each input is something you can check or test.
A good habit is to do both and see whether they roughly agree. If they differ by a factor of ten, one of your assumptions is wrong.
Why market sizing circles can mislead
The title of this piece comes from a common critique: market sizing frameworks can encourage small thinking, or false precision. There are a few traps.
- Defining the market by what exists. New products often create markets that didn’t exist before. Ride-hailing’s market wasn’t the taxi industry. Counting only today’s spending can understate the opportunity.
- Defining the market too widely. Claiming a vast TAM by including adjacent categories you won’t serve makes a deck look big and says nothing.
- Treating the number as destiny. A large market does not guarantee you can capture any of it.
- Ignoring willingness to pay. People using a free alternative may never become customers.
- False precision. A figure like $4.37 billion implies accuracy that doesn’t exist.
Investors know all this. A deck with a ludicrous TAM can come across as naive. Better to show a smaller, well-reasoned number and an explanation of how the company expands.
A better way to use market sizing
Instead of treating the three numbers as a ritual, treat them as a way to examine your assumptions.
- Start with who the first customers are and why they’d buy. Make that segment concrete.
- Estimate the first beachhead in detail: how many are there, what do they pay, how do you reach them?
- Describe the path to expand: new customer types, new features, new regions.
- Show the logic from beachhead to larger market, and mark which steps are guesses.
- Check that the beachhead alone can support a real company. If it can’t, you need a plan for what comes next.
How to explain it in a pitch
Keep it short and specific. State your initial target, the number of customers, the average revenue and the reasoning. Then explain how you grow. A founder who can say “here are the 40,000 businesses we can reach today, here is what they pay, and here is how we move to the next group” is more convincing than one who shows a trillion-dollar circle.
Good market sizing invites questions rather than avoiding them. Be ready for the obvious ones: how did you get these numbers? What would change them? What are you assuming about adoption speed?
Common questions
Does market sizing need all three numbers? Not always, but investors expect you to understand the concept. Is bigger better? Only if it is credible. What about early-stage or experimental ideas? Focus on evidence of demand, such as waiting lists, pilots and conversations, since the numbers are rough at that point. Investors weighing an early deal, as described in our piece on what a seed round means for founders, care more about that evidence than about a trillion-dollar circle.
The takeaway
Market sizing is useful vocabulary and a poor oracle. TAM, SAM and SOM help you think, but they cannot predict. Define them clearly, build them from the bottom up, and spend more time on the story of who buys first and why. A modest, well-defended market beats a grand, hand-waved one every time, and honest market sizing is the first step toward showing why.
