Serviceable obtainable market (SOM): how to size the number that should actually drive your targets

A total addressable market number looks impressive on a board slide and tells a sales rep almost nothing about her Monday. She still has a named list, a quota, and about forty hours to work it. What decides whether she hits her number is not how big the market could theoretically become. It is how many of those accounts she can actually win this year, against the competitors already sitting inside them, with the team you have on payroll right now.

That figure has a name. The serviceable obtainable market, or SOM, is the share of your serviceable market you can realistically close in a defined period. It is the smallest of the three market numbers, and it is the one that should be driving your hiring plan and your territory map. Most companies never calculate it. They take a big TAM, apply a round percentage, and call the result a target.

We tend to get called in after that has already gone wrong. A company sizes a huge market, builds quota on it, and watches the team miss for three straight quarters. The number was never real, because nobody did the capacity math behind it. This is the deep dive that sits under our TAM, SAM and SOM guide; if you want the sizing exercise for the middle number, read the serviceable addressable market piece alongside this one.

What serviceable obtainable market (SOM) actually is

Start from what SAM already gave you. Your serviceable addressable market is the set of accounts that could plausibly buy from you: the right segment, a geography you can sell into, a product that fits their problem. SOM takes that pool and asks a harder question. Of all those accounts, how many will realistically choose you inside a set window, usually a year, once you account for the competitors who got there first and the fact that your reps can only run so many deals at once.

So SOM is bounded by four things at the same time. Sales capacity, meaning how many opportunities your people can genuinely carry. Your historical win rate against the competitors who show up in those deals. The buyer's budget and buying cycle, which decides how many accounts are even in-market this year. And the length of the period you are measuring. Change the period and the number changes, which is why an SOM figure without a timeframe attached is meaningless.

Calculating SOM from SAM: capacity, win rate, reality

There are two ways to get to a serviceable obtainable market number, and the honest answer uses both as a cross-check.

The first is top-down. Take your SAM and multiply it by a defensible share, informed by where you actually rank against the incumbents and how much of the market is genuinely up for grabs this year rather than locked into renewals. This is quick and it is the version most decks stop at, which is exactly why so many of them are wrong.

The second is bottom-up, and it is the one that keeps you honest. Work it from capacity. Take the number of reps you will have, multiply by the deals one rep can carry through a full cycle in the period, and you get the number of opportunities the team can actually run. Apply your real closed-won rate to that. What comes out is the count of new customers you can win, which you multiply by average deal size to reach a revenue SOM. If the top-down number is three times the bottom-up number, the top-down number is a wish.

A worked shape makes it concrete. Say a rep can carry roughly thirty live opportunities to a decision across a year, and you have five reps. That is around a hundred and fifty real shots. If your win rate against your usual competitive set is one in four, you are winning something under forty accounts, not the four hundred your SAM percentage implied. Multiply those forty by your average contract value and you have a SOM you can actually staff, quota, and defend in a forecast review.

SOM vs SAM: the difference that trips people up

SAM and SOM get blurred together constantly, and the blur is expensive. SAM answers who could buy from you. SOM answers who will, given that you are not the only vendor calling and your team has a finite number of hours. SAM is a property of the market. SOM is a property of your company inside that market this year.

The gap between the two is where most go-to-market plans quietly break. A SAM of, say, several thousand fitting accounts feels like abundance. But if only a fraction are in-market this cycle, and you win a quarter of the ones you compete for, and you can only work a few hundred of them with the reps you have, your obtainable number is a small corner of that SAM. Naming that corner honestly is the whole point of the exercise. The plumbing analogy people reach for here does you no favours; this is arithmetic, not intuition.

Why SOM, not TAM, should set targets and territory

TAM is a fundraising number. It tells an investor the ceiling is high enough to be worth backing, and for that job it is fine. The trouble starts when TAM leaks out of the pitch deck and into the operating plan.

Quota should come off SOM, because SOM is the only figure built from what your team can physically do. Territory design should come off SOM too, so that every rep is handed a patch with enough obtainable accounts to make their number without stealing from the rep next to them. Hiring math is the same story in reverse: if your SOM says you can win forty accounts and your plan needs eighty, you have a headcount decision to make, not a motivation problem. When we run TAM mapping for a client, the SOM layer is the part that actually changes how they staff the year.

The fantasy SOM that props up a broken quota

Here is the pattern we see most. Someone needs the plan to reach a revenue number that was set before anyone sized the market. So the SOM gets reverse-engineered to fit the target. Win rate gets rounded up. Capacity gets assumed rather than counted. The number of in-market accounts gets treated as if the whole SAM were buying this quarter.

The quota that falls out of that looks ambitious in a spreadsheet and lands as an impossible ask on the rep. She works the list, hits the real win rate, and comes up short through no fault of her own. Three quarters of that and your best people start updating their profiles. The cost here is not the missed number in isolation. It is that you cannot tell whether you have a market problem, a product problem, or a capacity problem, because the plan never measured any of them. A SOM built from real capacity and real win rate protects the team from carrying a target the math never supported.

What SOM tells you about who to call first

A realistic SOM does more than size a target. It forces prioritisation, because once you accept you can only win a few dozen accounts this year, the question stops being how big the market is and becomes which accounts to work. That is where market sizing and account selection meet.

The accounts inside your obtainable number should be the ones where you win most often: the segment that closes fastest, at a healthy rate, and stays. Sizing SOM usually surfaces a segment that looks large in the SAM and almost never converts, and the right move is to take those out of the reps' priority list rather than let them absorb capacity you cannot spare. The sharper your definition of your ICP, the tighter that SOM becomes and the shorter the list of accounts your team should call on Monday morning. A smaller, truer number that the team can actually hit beats a large one that quietly sets them up to fail.

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