TAM, SAM and SOM

What TAM, SAM and SOM mean

Each number sits inside the one before it, like circles inside circles. Investors look at all three, but the one that matters most for a new business is SOM, because it's the revenue you might actually make.

TAM: total addressable market

The total yearly revenue if every possible customer bought a product like yours. It's the ceiling, and nobody gets all of it.

SAM: serviceable available market

The part of TAM you can actually serve with your product, price, language and sales channels. Some people call it the serviceable addressable market; it means the same thing.

SOM: serviceable obtainable market

The part of SAM you can realistically win in the next three to five years, given your competitors and how fast you can reach people.

Top-down vs bottom-up

There are two ways to get these numbers. Top-down starts from a big figure, usually from an industry report, and cuts it down: “The invoicing software market is $5 billion, small businesses are 30% of it, we'll win 1%.” It's quick, but the result depends on a report you didn't check and percentages you picked.

Bottom-up starts from customers: count the people or businesses who have the problem and multiply by what one of them would pay in a year. It takes longer and the result is usually smaller, but you can explain every number in it. Investors trust bottom-up figures more for exactly that reason.

A worked example, bottom-up

Say your idea is a tool that chases late invoices for small design and marketing agencies. The numbers below are made up to show the math. For your own idea, use real counts: government business statistics, professional network searches, directory listings or the member counts of trade groups.

1. Count everyone with the problem. Say there are 400,000 small agencies in the countries you could sell to one day. At $50 a month, or $600 a year, TAM is 400,000 × $600 = $240 million a year.
2. Cut it to who you can serve. Your first version only works in English with two popular invoicing tools, and you'll only market in the US and UK. That leaves 60,000 agencies. SAM is 60,000 × $600 = $36 million a year.
3. Estimate what you can win. With one strong competitor and a small budget, winning 2% of SAM in three years is ambitious but possible: 1,200 agencies. SOM is 1,200 × $600 = $720,000 a year.

What the example tells you

A $240 million TAM sounds exciting, but the useful number is the $720,000 SOM. For a solo founder or a small team, that's a good business. For a startup hoping to raise venture money, it's too small, unless the product can grow into more countries, more customer types or a higher price.

That's the real value of the exercise. It doesn't predict revenue. It shows which assumptions matter most, such as the price, the number of customers you can reach and the share you can win, so you can test those first.

Common mistakes

The 1% fallacy

“If we get just 1% of a $10 billion market…” Nobody gets 1% of a market by default. Share is won customer by customer, so show how you'll reach them.

Counting people who don't have the problem

Not every small business needs an invoicing tool. Count only those with the problem, such as agencies that bill clients after the work is done.

Using a price nobody has paid

Your price is a guess until someone pays it. Test it before you build the model on it.

Treating TAM as a goal

TAM is a ceiling, there for context. Plans and forecasts should start from SOM.

How investors read these numbers

Investors use TAM to judge whether a company could become very large if everything goes right, so venture-backed startups usually need a TAM in the billions. They use SAM and SOM to judge whether your plan is grounded. A bottom-up model with a modest SOM and a clear path to grow it is more convincing than a giant top-down TAM.

If you're not raising money, you can skip the big TAM entirely and ask a simpler question: are there enough customers I can reach, at a price they'll pay, to give me the income I want? If 300 customers at $50 a month would make you happy, your job is to find out whether 300 such customers exist and how to reach them.

Market size isn't demand

A market can be big on paper and still not want your product. Market size tells you how much there is to win if people want it. It can't tell you whether they do. That takes evidence from people with the problem: posts where they ask for a fix, conversations, and sign-ups on a page with a price.

So do both, in order. A quick bottom-up estimate tells you whether the idea is worth testing. A test tells you whether the estimate's customers exist and act. Then you can redo the numbers with a real conversion rate and a real price instead of guesses.

Test demand with a landing page