TAM SAM SOM Calculator
Investors and boards do not fund a market — they fund the slice of it you can actually win. Enter your total market and two honest percentages to turn a huge TAM into the SOM that should drive next year’s plan.
TAM, SAM, SOM is a nested market-sizing model. TAM (total addressable market) is everyone who could ever buy. SAM = TAM × the share you can actually serve, given geography, product fit and segment. SOM = SAM × the share you can realistically capture near-term, given your reach, sales capacity and competition. SOM — not TAM — is the number that should size your revenue plan; always sanity-check it bottom-up with accounts × average contract value.
TAM SAM SOM Calculator inputs and result
How to use this calculator
- Size your TAM honestlyEstimate the total annual revenue if every possible buyer in your category bought. Build it two ways and reconcile: top-down from industry reports, and bottom-up from total potential buyers times average annual spend. A TAM that only exists top-down is usually inflated.
- Set the serviceable shareEnter the percentage of that total you can actually serve today — limited by where you sell, which segments you fit, and what your product covers. A US-only SaaS product cannot count global TAM as serviceable. This gives you SAM.
- Set the obtainable shareEnter the percentage of the serviceable market you can realistically win in the next few years, given your sales capacity, brand, channels and competition. This is the hardest number to be honest about — and the most important. It gives you SOM.
- Read the funnel and SOMThe tool shows TAM, SAM and SOM as a shrinking funnel. SOM is the figure that should anchor your revenue and headcount plan — not the headline TAM. Treat TAM as the ceiling, SOM as the target.
- Sanity-check bottom-upCross-check the SOM: realistic accounts you can reach times your average contract value should land near it. If the two methods disagree by an order of magnitude, your percentages are off. Export the CSV for your model and deck.
RGM Expert Says
The mistake we see in nearly every pitch deck is leading with a giant TAM and treating it as the prize. A $50 billion TAM tells an investor almost nothing useful, because no company captures its whole market. The number that earns credibility is the SOM — the slice you can plausibly win in the next few years — because it is the only one that connects to a real plan for revenue, headcount and spend. We coach founders to lead with SOM and use TAM only to show the ceiling.
The two percentages are where honesty lives or dies. Serviceable share is usually a question of fact: where you can sell, which segments you fit, what your product actually covers. Obtainable share is a question of nerve — it is the number people inflate to make the model look exciting. We pressure-test it against sales capacity and competition: if you have eight reps and a 12-month sales cycle, your obtainable share next year is small, and pretending otherwise just sets up a miss.
The discipline that saves models is reconciling top-down and bottom-up. Top-down (industry report × your percentages) is fast but easy to fudge; bottom-up (real reachable accounts × average contract value) is grounded but easy to under-scope. When the two land in the same neighborhood, you have a defensible SOM. When they are an order of magnitude apart, one of them is fiction — and finding out which is the whole value of doing both.
How it works
The model is multiplicative and nested: each layer is a percentage of the one above it. TAM is the full market; multiply by the serviceable share to get SAM; multiply SAM by the obtainable share to get SOM.
- TAM — total annual revenue if every possible buyer bought.
- Serviceable share — % of TAM you can serve (geography, fit, segment) → SAM.
- Obtainable share — % of SAM you can realistically win near-term → SOM.
- Bottom-up check — reachable accounts × average contract value, compared to SOM.
There is no ‘correct’ serviceable or obtainable percentage — they depend entirely on your business. The TAM–SAM–SOM structure is a standard market-sizing framework taught in business strategy; always reconcile the top-down estimate with a bottom-up build to keep it honest.
Why SOM matters more than TAM
A big TAM is the easiest number to inflate and the least useful to act on. Every market looks enormous when you count everyone who could theoretically buy. The discipline of SAM and SOM is what turns that headline into a plan: SAM asks what you can actually serve, and SOM asks what you can actually win. Boards and investors have learned to skip past TAM and ask, ‘what is your obtainable market?’ — because that is the number tied to revenue.
The model also exposes wishful thinking. If your SOM comes out as a large fraction of TAM, your percentages are almost certainly too generous — few companies ever capture a big share of a real market. A SOM that is a fraction of a percent of TAM is normal and credible. The funnel shape is supposed to narrow sharply; when it does not, the estimate is the problem.
Finally, top-down and bottom-up are two different lenses on the same market, and the gap between them is information. Top-down sizing (reports times percentages) is quick but soft; bottom-up sizing (real reachable accounts times average contract value) is concrete but easy to under-scope. Doing both — and reconciling them — is what separates a defensible SOM from a number invented to fill a slide.
Top-down vs bottom-up sizing
There are no universal benchmark percentages for SAM and SOM — they are specific to your market. What is universal is the discipline of building the estimate two ways. Here is how the two methods compare.
| Method | How you build it | Strength / risk |
|---|---|---|
| Top-down | Industry TAM × serviceable % × obtainable % | Fast; risk of inflated percentages |
| Bottom-up | Reachable accounts × average contract value | Grounded; risk of under-scoping reach |
| Reconciled | Use both; investigate large gaps | Defensible; the gap itself is the insight |
What investors and operators say
Do not tell me the market is a billion dollars. Tell me which customers you can reach next year and what they will pay — that is the number I can underwrite.
Bottom-up sizing built from real, reachable accounts beats a top-down number every time, because you can defend every line of it.