TAM SAM SOM Calculator
The three market tiers built two ways at once — down from the figure you were going to cite, and up from customers you can actually count. When the two disagree, that gap is the only thing on the slide worth talking about.
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Every TAM SAM SOM calculator narrows one number down through three tiers. This one builds the top tier twice — once from the report you were going to cite, once from customers you can actually count — because when those two disagree, that is the only thing on the slide worth discussing.
The analyst or industry figure you were going to cite.
Companies or people who could plausibly buy.
What one of them pays you a year.
Of the market, how much your product actually serves. TAM → SAM.
Of that, how much you could realistically win. SAM → SOM.
Top-down
From the published figure
Bottom-up
2,500 customers × $50K
The published figure is 4.0× larger than what you can count — a gap of $375.0M. The two methods are some way apart. Somebody will ask which one you believe, so decide before the meeting and lead with the bottom-up build.
| Tier | Top-down | Bottom-up | What it means |
|---|---|---|---|
| TAM | $500.0M | $125.0M | Everyone who could ever buy this |
| SAM | $250.0M | $62.5M | Those your product actually serves |
| SOM | $50.0M | $12.5M | What you could realistically win |
The serviceable and obtainable percentages are judgements, not measurements — and they are where a market slide is usually wrong. Two multiplications by a number someone invented turns any TAM into any SOM. Write down why you chose them.
A market slide is a claim about a product that does not exist yet. If you are building it largely on your own, Tekk turns what you want into specs your coding agent can actually execute.
The three tiers
TAM = customers × annual contract value
SAM = TAM × serviceable share
SOM = SAM × obtainable share
TAM — everyone who could ever buy a product like yours. SAM — the share your product actually serves, once geography, segment and use case are applied. SOM — what you could realistically win in the forecast period.
Worked example
2,500 target customers at $50,000 a year, half of them serviceable, a fifth of those obtainable:
| Tier | Working | Result |
|---|---|---|
| TAM | 2,500 × $50,000 | $125.0M |
| SAM | $125.0M × 50% | $62.5M |
| SOM | $62.5M × 20% | $12.5M |
Multiple segments are sized separately and added. A second segment of 200 enterprise accounts at $400,000, 25% serviceable and 10% obtainable, contributes $80.0M of TAM and $2.0M of SOM — giving a combined SOM of $14.5M across the two.
Averaging the segments instead would produce a figure describing neither.
The gap is the signal
Every tool on this subject narrows one number through three tiers. The tiers are two multiplications; there is nothing to get wrong and nothing to learn.
What is worth knowing is whether the number you started with survives being rebuilt from scratch:
| Top-down ÷ bottom-up | What it means |
|---|---|
| Under 1.5× | The two methods agree. Unusually strong — keep it. |
| 1.5–3× | Normal. Analyst figures count adjacent spend you cannot address. |
| 3–10× | Some way apart. Decide which you believe before the meeting. |
| Over 10× | Measuring a different market. Stop citing the report. |
On the defaults above, a published $500M figure against a $125M bottom-up build is 4.0× apart — a $375M gap, and squarely in the band where somebody will ask which number you actually believe.
Where market slides go wrong
The percentages are invented. Two multiplications by a number nobody justified will turn any TAM into any SOM. If the serviceable share does not follow from a real constraint — one region, one company size, one workflow — it is decoration.
The report is doing the work. Every company in your category is citing the same analyst figure. It is the weakest evidence on the slide precisely because it required nothing of you.
Bigger is assumed to be better. A defensible $200M beats an indefensible $50B, because the second one invites a conversation about your judgement rather than your market.
Units instead of revenue. TAM is a money figure. Counting seats without a price produces something that cannot be compared to anything, including your own revenue.
How it works
- 1
Put in the number you were going to quote
The analyst figure, the industry report, the one in the deck template. That is your top-down TAM, and on its own it is the weakest kind of evidence — every company in your category is citing the same one.
- 2
Then build it from the bottom
How many customers could plausibly buy, and what one pays a year. Multiply them and you have a TAM you can defend line by line. This TAM SAM SOM calculator runs both and puts them side by side rather than making you pick.
- 3
Read the gap, not the tiers
The tiers are arithmetic and every market size calculator produces them. The useful output is the ratio between the two TAM figures: close together and you have a strong slide, an order of magnitude apart and one of the numbers is measuring a different market.
Frequently asked questions
- What do TAM, SAM and SOM mean?
- Total Addressable Market is everyone who could ever buy a product like yours. Serviceable Available Market is the share your product actually serves — the right geography, segment and use case. Serviceable Obtainable Market is what you could realistically win in the forecast period, given competitors and your own capacity.
- How do you calculate TAM SAM SOM?
- The TAM SAM SOM calculator above works down through three multiplications. TAM is customers multiplied by annual contract value. SAM is TAM multiplied by the share you can serve. SOM is SAM multiplied by the share you could win. 2,500 customers at $50,000 gives a $125M TAM; at 50% serviceable and 20% obtainable that is $62.5M SAM and $12.5M SOM.
- What is the difference between top-down and bottom-up market sizing?
- Top-down starts with a published market figure and narrows it. Bottom-up starts with countable customers and multiplies up. Top-down is fast and unfalsifiable; bottom-up is slower and defensible. Running both is the point of this TAM SAM SOM calculator, because the disagreement between them is more informative than either number alone.
- Which method should I use in a pitch?
- Lead with bottom-up and mention top-down for context. Investors have seen the same analyst figure in every deck this month, and a number built from customers you can name is the one that survives the follow-up question. Present the top-down figure as corroboration, not as the claim.
- What if the two numbers are wildly different?
- Then one of them is measuring a different market, and it is usually the top-down one. Analyst figures routinely count adjacent spend — services, incumbents' whole product lines, budget nobody in your segment would ever route to a product like yours. A gap of two or three times is normal; ten times means you should stop citing the report.
- Is a market size calculator enough for a fundraise?
- No, and no market size calculator can be. What it produces is a number; what an investor is assessing is whether you understand who buys and why. The arithmetic takes a minute and the reasoning behind the serviceable and obtainable percentages takes considerably longer — that is the part that gets scrutinised.
- What percentages should I use for SAM and SOM?
- There is no standard, which is precisely the problem. Serviceable share should follow from a real constraint — you only sell in one region, or to one company size, or your product handles one workflow. Obtainable share should follow from competitors and your own capacity to sell. If you cannot say why the number is what it is, it is decoration.
- How big does a TAM need to be?
- Venture investors commonly look for a TAM large enough to support a very large outcome, which in practice means talking about billions. That expectation is also why TAM figures get inflated, and why a bottom-up build that lands lower but holds up is often the better slide. A defensible $200M beats an indefensible $50B.
- Should I use revenue or units?
- Revenue, always. TAM is a money figure, so customers must be multiplied by what they pay annually. Counting units or seats without a price attached produces a number that cannot be compared to anything, including your own revenue.
- How do I handle multiple customer segments?
- Size each segment separately and add the results. Enterprise and SMB have different contract values, different serviceable shares and different obtainable shares, so averaging them produces a figure that describes neither. Run this tool once per segment and sum the SOM figures.
- Does TAM change over time?
- Yes, and a growing TAM is often a stronger argument than a large one. A market expanding 20% a year is a different proposition from a static one of the same size, and the more useful framing is where the market will be when you are ready to serve it rather than where it is today.
- Do you store the numbers I enter?
- No. The calculation runs entirely in your browser. Nothing is sent to a server, nothing is logged, and there is no account — which is worth knowing before you type an unannounced market strategy into a web page.
- Why is this free, and what is Tekk?
- Tekk is a spec-driven development platform for people building software with AI coding agents. This calculator costs us nothing to run, and the founders writing a market slide are usually the same people building the product. No signup, no run limit, no upsell inside the tool.
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