Market sizing gets a bad reputation because people approach it wrong. They chase a headline TAM number to impress investors, then build a go-to-market plan that quietly contradicts it. TAM, SAM, and SOM are only useful when each figure is grounded in something you can actually defend.
What the three numbers actually mean
TAM (Total Addressable Market) is the theoretical ceiling: the revenue available if every possible buyer in the world chose your product or service. SAM (Serviceable Addressable Market) narrows that to the buyers you can realistically reach, given your geography, distribution, and product scope. SOM (Serviceable Obtainable Market) narrows further to the share you can realistically win in the near term.
Most confusion happens because teams treat all three as the same exercise done at different scales. They are not. Each one answers a different question, and blurring the distinctions produces numbers that don’t connect to real decisions.
- TAM answers: what is the total pool of spend in this category?
- SAM answers: which portion of that pool can we actually serve?
- SOM answers: what portion of SAM can we realistically capture in the next 12—24 months?
Getting this wrong in a pitch deck is recoverable. Getting it wrong in your actual planning costs real money.
Two approaches to calculating TAM
There are two common methods, and they belong in different situations.
Top-down
Top-down market sizing starts with published industry data and works inward. You find a research report, a trade association estimate, or analyst data for the total category, then apply filters (geography, segment, price band) until you arrive at your slice.
It’s fast and it signals familiarity with the competitive landscape. The problem: the number often includes buyers who will never purchase your specific product, and third-party research rarely slices the market the way your product does. Top-down TAM tends to be impressive and imprecise.
Bottom-up
Bottom-up sizing starts with buyer behaviour. Count the addressable buyers, estimate how much spend each represents per year, and multiply.
For a B2B SaaS tool: how many companies fit your buyer profile, how many seats does each typically buy, and what do you charge per seat? This builds a number you can defend because each assumption is explicit and testable. When you run a bottom-up calculation and the result looks smaller than you expected, that is information, not a problem to paper over.
The bottom-up number that makes you nervous is more useful than the top-down number that makes you feel good.
For most early-stage planning, use bottom-up for SAM and SOM, and top-down as a sanity check on TAM.
Sizing your SAM
SAM is where operational reality bites. The filters that shrink TAM into SAM are things like:
- Geography. If you can only serve English-speaking markets right now, remove the rest.
- Distribution. If you sell direct and have no channel partners yet, cut segments you can only reach through resellers.
- Regulatory eligibility. If certain industries are off-limits until you get a certification, remove them from the count.
- Product fit. If your current product only solves the problem for companies above a certain size, narrow accordingly.
Each filter should have a real reason, not just a wish to look focused. The tighter your SAM, the more confident you can be in your SOM, and the more your planning will reflect something achievable. Vague SAM filters produce go-to-market strategies that spread effort too thin.
How to estimate SOM honestly
SOM is the number founders most often inflate, because the instinct is to look optimistic. A more useful question: what is the realistic capture rate for a company at your stage, with your current sales capacity and marketing reach?
Comparable benchmarks. Look at companies that were at the same stage in a similar market. What share of their SAM did they capture in the first two years? This is hard to find precisely but worth estimating from what’s public. The go-to-market strategy you choose shapes this number significantly; a product-led approach and a direct sales approach will produce very different capture rates from the same SAM.
Sales capacity. If you have two salespeople who can each close a set number of accounts per quarter, your SOM is roughly constrained by that ceiling. The market can be large; what matters is how much of it you can physically reach and convert. Optimistic SOM figures usually assume sales capacity that doesn’t exist yet.
Revenue targets, reversed. If your 12-month revenue target is a specific number, divide it by your average contract value. That is your required customer count. Now check whether that count is a credible share of your SAM. If it implies a 40% share in year one, something needs revisiting.
What to watch out for
A few pitfalls are worth naming plainly.
Confusing desire with access. Not every company that could benefit from your product has the budget, the decision-making process, or the urgency to buy right now. Potential interest is not addressable demand.
Stale data. Industry reports age fast. A TAM figure from a 2021 report may not reflect category shifts since then. Always date your sources and note how recently the underlying data was collected.
Ignoring incumbents. Your SOM is not just a function of product quality. It’s a function of what you’re taking from someone else. If an entrenched player holds a large share of your SAM, your realistic SOM is further constrained. This is part of why competitive landscape work belongs in the brand launch plan, not as an afterthought.
Using SOM to justify the wrong strategy. A small SOM is not always a problem. A small, high-margin SOM with genuine pricing power is a stronger starting point than a large, commoditised one. If you’re thinking through how to price, value-based pricing for services connects directly to how you should think about this.
How Strynal approaches market sizing
Market sizing is input to strategy, not a slide to polish once the strategy is set. The numbers you land on for SAM and SOM determine which segments to prioritise, which channels make sense, and how aggressively to price. Work through them early, and the strategy and positioning work that follows has a foundation to build on.
When clients arrive with sizing already done, we walk through the assumptions. The SAM filter list and the SOM calculation are where the real disagreements live. A SAM figure that survives stress testing is worth far more than a large one that falls apart in the first investor question. If your market sizing is holding up scrutiny in pitch meetings but not actually driving your planning, that is a signal that the two exercises have drifted apart.