TAM, SAM and SOM: The Assumptions Are the Deliverable
SRF Capital Studio Research DeskFunding Intelligence, SRF Capital StudioThree nested estimates, the only defensible way to build them, and why the largest of the three is usually the least useful.
Summary
- TAM is the total market if everyone who could buy did. SAM is the part reachable with the product, channel and geography actually operated. SOM is the share realistically winnable in the planning period.
- Build bottom-up. Top-down sizing, which takes a published industry figure and applies a percentage, is recognised immediately by anyone who reads these for a living.
- TAM is usually irrelevant to the decision in front of the business. SAM and SOM are the two that carry weight.
Three nested numbers, and who asks for them
The three sit inside each other. The total addressable market is everyone who could conceivably buy the thing. The serviceable addressable market narrows that to the part actually reachable given what the company sells, where it sells it and how. The serviceable obtainable market narrows again to what could realistically be won inside the planning horizon.
It is worth being honest about where the request comes from. Promoters rarely ask for a TAM. Investors do, and that is almost always the origin of the exercise. The number is being built for a fundraising conversation rather than an operating one, and knowing that shapes how it should be presented.
Two other moments earn it a place. One is entering a category so new that no served-market history exists. The other is sizing a new product or geography before capital is committed.
Building the number from the bottom up
Bottom-up means starting from units of demand that can be counted and multiplying up, rather than starting from a large published figure and cutting it down.
- Define the unit of demand. Customers, procedures, tonnes, transactions. Choose the one the business actually sells in.
- Build the base. Number of potential buyers, multiplied by purchase frequency, multiplied by a realistic price.
- Narrow to SAM. Apply the real constraints: geography served, channel reach, product fit, regulatory limits.
- Narrow to SOM. Use observable competitor share and the company's own coverage today.
- State every assumption on the same page as the number. Not in an appendix, and not in a footnote.
The last step is the one that gets skipped and the one that matters most. A market size is entirely a function of its assumptions, which means the assumptions are the deliverable and the number is a consequence of them.
The number is a consequence. The assumptions are the deliverable.
Narrowing to what you can actually serve
The step from TAM to SAM is where most of the honesty lives, because it is where a company writes down what it cannot currently reach.
A manufacturer selling through two distributors in four states does not address a national market, whatever the category figure says. A product with a regulatory approval covering one use does not address the adjacent uses. A channel that reaches modern trade does not reach the general trade next to it.
Each of those constraints is a decision the business could revisit, which is what makes the SAM number useful. It converts an abstract opportunity into a list of things that would have to change, and those are the things a plan can actually contain.
SOM then narrows once more, and it is the number a management team should be held to. It is bounded by what competitors already hold, by how much of the market the company's coverage reaches at all, and by how quickly a share position can realistically move. Share shifts slowly in most categories, and a plan assuming otherwise is usually assuming a competitor will cooperate.
A useful discipline at this step is to name the customers who make up the first slice of SOM. If a sizeable obtainable market cannot be described in terms of identifiable buyers or an identifiable channel, the narrowing has been arithmetic rather than analysis.
Top-down sizing and why investors spot it
Top-down sizing takes a published industry figure and applies a percentage to it. It is how this framework is most often misused, and a competent investor spots it at once.
The tell is the arithmetic. A slide that says the market is worth a large round number and that capturing one percent of it produces a comfortable business has not sized anything. It has asserted that a small share of a big number is also a big number, which was never in doubt.
There is a legitimate use for the top-down figure: as a cross-check. Build bottom-up, then compare the result against the published estimate and explain the gap. If the two are far apart, one of them is wrong and finding out which is useful work. Presenting the top-down figure as the build itself is what damages credibility.
Published Indian market figures deserve particular care in that comparison. Many are assembled from a mix of survey work, association estimates and extrapolation, and the methodology is often not disclosed. Two reputable sources can differ by a multiple for the same category in the same year, which is a reason to treat either as a range rather than a fact.
The assumptions are the deliverable
Three limitations follow from that, and each one changes how the output should be presented.
- TAM is almost always irrelevant to the decision at hand. It is the number most often shown and the one least often used. SAM and SOM are what a plan is built on.
- The number moves with its assumptions. Change the price point or the purchase frequency and the answer changes by a multiple, which is why the assumptions travel with it.
- It encourages false precision. A market size carried to two decimal places claims an accuracy the method cannot support. Present ranges, and say what drives the width of the range.
A sizing exercise that arrives as a single confident figure has usually hidden its own uncertainty. One that arrives as a range with its drivers named is more useful and, in front of an investor, considerably more persuasive.
The presentation follows from that. Show the build, not just the result. One slide with the unit of demand, the buyer count, the frequency and the price does more for credibility than a large number on its own. It also gives a sceptical reader something specific to push on, and a specific objection is far easier to answer than a general doubt about the whole deck.
When served-market work beats a TAM slide
For an established business in a known market, market sizing is usually the wrong tool. Served-market work is more useful and more honest.
The reason is simple. An established company already knows who buys the category, because it sells to them. The open question is not how large the opportunity could theoretically be. It is why the company holds the share it holds, and what would have to change to hold more. That is a decomposition question rather than a sizing one.
Sizing also sits alongside the structural work rather than replacing it. A large market that is structurally unprofitable is not an opportunity, which is what Porter's Five Forces is for. A market's stage then decides how much of it is still available, which is what the industry lifecycle answers. Where a sizing exercise is genuinely the right starting point, it usually runs inside a strategy sprint.
Frequently asked questions
What is the difference between tam, sam and SOM?
TAM is everyone who could buy. SAM is the portion reachable with the product, channels and geographies the business actually operates. SOM is the share winnable within the planning period. Each is a narrowing of the one before it, and each narrowing should be justified by a named constraint.
How do you calculate TAM bottom-up?
Count the potential buyers, multiply by how often they buy, multiply by a realistic price. The discipline is in the second and third terms: purchase frequency and achievable price are where optimistic sizing hides, and both should be evidenced rather than assumed.
Is a bigger TAM always better in a fundraise?
No. An implausibly large TAM invites scrutiny of everything else in the deck. A smaller, well-evidenced SAM with a credible route to a defined SOM reads as a company that understands its own market, which is the impression actually worth creating.
How precise should a market size be?
Precise enough to support the decision and no more. Ranges, with the assumptions that set their width stated alongside. False precision is the most common flaw in this work and the easiest for a sophisticated reader to find.
How useful was this article?
One tap. It tells us what to write more of.
About the author
SRF Capital Studio Research Desk
Funding Intelligence, SRF Capital Studio
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