TAM, SAM, SOM: how to calculate your market size

Most business plans in Romania start from one impressive number, the e-commerce market passed 9 billion euros in 2024. Then someone says that capturing just 1% of it means 90 million euros. This is exactly the mistake the TAM, SAM, SOM model fixes.

TAM, SAM and SOM are three estimates of market size, from the broadest to the most realistic. They keep you from confusing the total market with the market you can actually reach, and they let you size your marketing budget, sales target and investor expectations correctly.

This guide covers what each term means, how to calculate them with two methods, a full worked example on a Romanian online store, what data sources to use for the local market, and the most common mistakes.

What do TAM, SAM and SOM mean?

TAM, SAM and SOM are three concentric circles. The big circle is the entire market. The middle circle is the part you can serve with your product and model. The small circle is the part you can realistically win in a given timeframe.

TAM (Total Addressable Market) is the total annual revenue a product or service category generates if you owned 100% of the market. It is the absolute theoretical ceiling, the answer to how big the opportunity is.

SAM (Serviceable Addressable Market) is the part of the TAM you can actually serve, limited by geography, the channels you sell in, the customer segment and your product range. It answers how much of the market fits my model.

SOM (Serviceable Obtainable Market) is the part of the SAM you can realistically win within 1 to 3 years, given your budget, competition, delivery capacity and channels. It answers how much I can actually take.

TAM is how big the cake is. SAM is the slice you can cut. SOM is how much you get to eat this year.

Why the distinction matters

Confusing TAM with SOM causes three concrete kinds of damage.

Oversized marketing budgets. If you set your sales target from the TAM, you will allocate budget for a level of demand that cannot actually reach you. Money burns on impressions to people who will never buy from you.

Unrealistic promises to investors. A pitch that says we capture 1% of a 9 billion market signals that the founder does not understand the difference between total and accessible market. Serious investors ask for SOM, not TAM.

Wrong channel prioritisation. When you know your current-year SOM comes from two counties and three product categories, you do not spread a national budget across the whole catalogue. You concentrate spend where the accessible market is dense.

How to calculate TAM, SAM and SOM, two methods

There are two approaches. The best estimates use both and check whether the results converge.

Top-down method

You start from a large market figure published by an external source and narrow it with successive percentages until you reach your segment. Fast, but it depends on the quality of the source and on how well you justify each percentage.

• Step 1, find the total category value (TAM) from a market report.
• Step 2, apply geography, channel and segment filters to get the SAM.
• Step 3, apply a realistic market share to get the SOM.

Bottom-up method

You start from your real units, number of potential customers, average price, conversion rate, and build upward. Slower, but far more credible for SOM, because it rests on your own performance numbers.

• Number of target customers x average order value x annual purchase frequency = revenue potential.
• For paid-media SOM, you start from budget, cost per click, conversion rate and average order value.

Use top-down for TAM and SAM, where you need the big figure. Use bottom-up for SOM, where you need a number you can actually deliver.

Worked example, a Romanian natural cosmetics online store

Take an online store selling natural and organic skincare and haircare, shipping across Romania. Here is what the three circles look like.

TAM, the total market

The Romanian cosmetics market is estimated at around 2 billion euros per year, all channels and all categories. The natural and organic segment is roughly 7 to 8% of that, so about 150 million euros per year. This is the TAM, everything that would be spent on natural cosmetics in Romania if a single store owned the entire category.

TAM = 150 million euros per year.

SAM, the market you can serve

The store sells only online and only in two sub-categories, skincare and haircare, no makeup or perfumes. We narrow the TAM with two filters.

• Online penetration of the category, about 28% of natural cosmetics sales happen online.
• The sub-categories sold, skincare and haircare cover roughly 55% of the natural segment.

SAM = 150 million x 0.28 x 0.55 = about 23 million euros per year. This is the realistic market your model can reach, customers buying online, in your categories.

SAM = 23 million euros per year.

SOM, the market you can win

For a new store with a limited budget and competition from established brands, a realistic share of the SAM over the first 3 years is 2%.

SOM = 23 million x 0.02 = about 460,000 euros per year at a 3-year horizon.

We check the figure bottom-up, through paid media, for year one. With a budget of 2,500 euros per month, a cost per click of 0.45 euros, a 2% conversion rate and an average order value of 55 euros:

• 2,500 euros / 0.45 euros = about 5,500 clicks per month.
• 5,500 x 2% = about 110 orders per month.
• 110 x 55 euros = about 6,000 euros revenue per month, so around 72,000 euros per year from paid media alone.

Adding organic, email and social, a realistic first year settles around 100,000 to 130,000 euros, well below the 3-year SOM. This is not an error, it is exactly the lesson, SOM grows over time, and the year-1 target is never the year-3 target.

If top-down and bottom-up give numbers that differ by tens of times, one of them has a wrong assumption. Find it before you build the budget on it.

Data sources for the Romanian market

Estimates are only as good as the sources. For the local market, these are the credible starting points.

• National Institute of Statistics (INS), data on population, incomes, retail trade, by county.
• Eurostat, European-level comparisons and e-commerce penetration by category.
• GPeC annual reports, the reference for the size and structure of Romania's e-commerce market.
• Statista and sector market reports, for the total value of categories (TAM).
• Google Keyword Planner, for the monthly search volume of keywords in your niche, a direct proxy for demand accessible through paid media.
• Your own numbers, cost per click, conversion rate, average order value, the best data for SOM.

Common mistakes

Confusing TAM with SOM. We capture 1% of a huge market is not a strategy, it is a hope. SOM is built bottom-up, from real channels and budgets.

Defining the TAM too broadly. If you sell natural cosmetics, your TAM is not the entire cosmetics market, it is the natural segment. An artificially inflated TAM weakens the plan, it does not strengthen it.

Ignoring bottom-up. A SOM calculated only top-down, as a percentage of a large market, says nothing about your real delivery capacity. Always verify bottom-up.

Treating the numbers as fixed. TAM, SAM and SOM are estimates, not truths. Refresh them yearly as the market and your numbers change.

How to use TAM, SAM and SOM in your marketing budget

The model is not a pitch-deck exercise, it is an allocation tool. The SOM tells you how big the realistic revenue target is for the current year. From there, you work backward to the budget.

If the year-1 SOM is 100,000 euros of revenue, and the average order value is 55 euros, you need about 1,820 orders. At a 2% conversion rate, that means roughly 91,000 visits from paid and organic channels. The paid-media budget is sized from this number of visits, not from an abstract market figure.

That is how the model becomes useful, not as a slide in a presentation, but as a chain linking the accessible market to the number of orders, to visits, to the monthly budget you put into Google and Meta.

What DAFE Digital does

Before we launch a campaign, we size the market accessible through paid media for your niche and geography, search volume, estimated cost per click and a realistic number of orders at the available budget. That is how we set a SOM target we can actually deliver, not a TAM figure that looks good on paper.

For related context, see how to allocate your advertising budget across channels and what a customer costs, acquisition cost and payback period.