TAM SAM SOM: How to Size a Market for a New Product
TAM, SAM and SOM are three nested estimates of a market’s yearly revenue: TAM is everyone who could buy your kind of product, SAM is the part your product can serve, and SOM is the part you can realistically win in the next 1 to 3 years. For a new product, SOM is the number that tells you whether the idea can pay you, because it counts only the buyers you can reach and win. Build it bottom-up, from buyers you can count and a price they already pay.
- TAM (total addressable market): yearly revenue if every possible buyer in the world bought your kind of product.
- SAM (serviceable available market): the part of TAM you can reach with your product as it is, in your channels and countries.
- SOM (serviceable obtainable market): the slice of SAM you can win against the competitors already there.
Why do market size slides look so convincing and mean so little?
You found a report that says the market for your category is worth billions. You take 1% of it, and the spreadsheet says you’ll be rich. Investors see that slide often, and plenty of founders who built something nobody bought started from it.
The number isn’t wrong. It just answers a different question: how much money moves in the category, not how much of it will reach you.
What does a wrong market size cost you?
A TAM-sized estimate makes every idea look worth building, so you stop filtering. You spend months on a product sized for a market you can’t reach: the wrong country, a buyer you have no channel to, or a price nobody in your segment pays. A bottom-up SOM done in an afternoon would have told you the realistic ceiling before you wrote a line of code or bought any stock.
What’s the difference between TAM, SAM and SOM?
| Size | Question it answers | How it’s built | What it’s good for |
|---|---|---|---|
| TAM | How big is the whole category? | Every possible buyer × yearly spend | Context, and whether the category is growing |
| SAM | How much can my product serve? | TAM filtered by your country, segment, channel and product type | Picking a segment and a geography |
| SOM | How much can I win soon? | SAM × the share you can reach and convert in 1 to 3 years | Deciding if the idea is worth building |
Each one sits inside the one above it. If your SOM is larger than your SAM, a filter is missing.
How do you calculate TAM, SAM and SOM bottom-up?
Bottom-up means counting buyers and multiplying by what they pay, instead of starting from an industry report. It’s slower, and it’s the version you can defend.
- Define one buyer. Not “small businesses”, but “solo bookkeepers in the US who invoice monthly”. See how to find a target market.
- Count them. Use public sources: government business statistics, association member counts, the size of the subreddits and groups where they gather, the number of sellers in a marketplace category.
- Set a yearly price. Use what they already pay competitors, not what you hope to charge. How to price a new product covers where to find it.
- TAM = all buyers of this kind, everywhere, × yearly price.
- SAM = only the buyers you can serve now (your language, your country, your channel, the platform you integrate with) × yearly price.
- SOM = SAM × the share you can win. Base the share on your channels: how many of them you can reach a year, and what fraction usually buys.
What does a worked example look like?
Here’s the math with round numbers, chosen only to show the method. Replace every one with a figure you can source.
- Product: a template pack for wedding photographers, sold once.
- Buyers worldwide who could use it: say 400,000 photographers who shoot weddings.
- Price: $50 once, so each buyer is worth $50 a year at most in year one.
- TAM: 400,000 × $50 = $20 million.
- You only sell in English, through Instagram and one marketplace, to photographers who edit in one app: say 60,000 of them.
- SAM: 60,000 × $50 = $3 million.
- In a year you can realistically reach 20,000 of them with content and ads, and say 2% of them buy: 400 sales.
- SOM: 400 × $50 = $20,000 in year one.
The TAM sounds like a business. The SOM tells you it’s a side product unless you add a second product, raise the price or find a cheaper way to reach more buyers. That’s the useful answer.
Top-down or bottom-up: which should you use?
Top-down starts from an industry report and narrows it with percentages. It’s fast, and it’s fine for TAM. The risk is that every percentage is a guess stacked on a guess.
Bottom-up starts from buyers you can count and a price they already pay. Use it for SOM, always. When the two methods land far apart, trust the bottom-up one and find out which top-down assumption broke.
Does a big market mean people want your product?
No. TAM measures money that already moves in a category. It doesn’t show that anyone wants your version, at your price, from you. Demand shows up in other places:
- People asking for it. Threads where buyers describe the problem in their own words. See how to find pain points on Reddit.
- Competitors spending on ads. Ads that have run for months in the Meta Ad Library mean someone is paying to sell it and it works.
- Buyers already paying. Reviews, sales counts and prices on marketplaces. See willingness to pay.
A small SOM with strong signals beats a huge TAM with none. Size the market to find the ceiling, then check demand to find out if there’s a floor.
FAQ
What is a good SOM for a startup?
One that covers your costs and pays you within the time you can wait. There’s no universal number. For a solo product, a SOM that can reach your target yearly income with realistic reach and conversion is a good start.
How do you calculate SOM?
Take SAM and multiply it by the share you can win in 1 to 3 years. Base that share on how many buyers your channels can reach and the fraction of them that usually buys, not on a flat 1%.
Is TAM yearly or total?
Yearly. TAM, SAM and SOM are all yearly revenue figures, so a one-time product counts what new buyers would pay in a year.
Do investors care about TAM, SAM and SOM?
Yes, they often ask for all three. They trust a bottom-up SOM with sources more than a large TAM from a report.
Check the demand behind your market size with Vettoz
Market size tells you the ceiling. Vettoz checks whether anyone is reaching for your idea now. Inside Claude, ChatGPT or Cursor, he reads Reddit, X, TikTok, YouTube, active Meta ads, Google, TikTok Shop and the App Store for one idea, counts the signals and scores it GO, TEST or RETHINK. Your AI writes the report with every source linked. Your first 2 checks are free, no card.
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