Total addressable market (TAM) is the total revenue available if every possible customer for your product or service bought it from you. It is a ceiling, not a forecast, and it is usually paired with two narrower figures: serviceable addressable market (SAM) and serviceable obtainable market (SOM).
How total addressable market works
The three figures sit inside one another. TAM counts everyone who has the problem you solve. SAM narrows that to the buyers you can actually reach and serve, given your location, channels, price point and any regulatory permissions you need. SOM is the share of SAM you could realistically win over the next few years, against the competitors already there.
There are two ways to size them. Top-down starts from a published industry figure and cuts it down by percentages. It is quick, but it inherits every assumption in the source report. Bottom-up counts actual buyers and multiplies by what each spends: the number of eligible businesses or households, times the share that buy this kind of thing, times their average annual spend. Bottom-up takes longer, but each number can be checked. For UK counts, the Department for Business and Trade’s business population estimates, Companies House data and ONS household spending tables are common starting points.
Take a hypothetical commercial cleaning firm in Bristol. Its TAM is every office in the UK that pays for cleaning. Its SAM is the offices its vans can reach within a sensible drive. Its SOM is the slice of those it could win, given its crew capacity, its prices and how many rivals already hold the contracts. Each step should be written down with its source, so someone else can test it.
Why it matters
For most UK businesses, the useful part is the narrower figures. SAM tells you whether your marketing is pointed at a market big enough to repay the effort. SOM tells you how much growth is plausible before you need a new product, a new region or a new type of customer. If SOM is small, doubling the ad budget runs into diminishing returns quickly, because there are only so many buyers to find.
Market size also shapes channel choice. A specialist B2B supplier whose SAM is a few hundred firms gets more from targeted outreach and content written for a precise ideal customer profile than from broad search campaigns. A consumer product with a large SAM can afford to test wider channels. Lenders and investors often ask for TAM, SAM and SOM, and they tend to trust a careful bottom-up SOM more than a large headline TAM.
Common mistakes
- Quoting a whole industry as your market. A national figure for the beauty sector says nothing about how many people will book a treatment at one salon in Croydon.
- Stopping at TAM. The figure that should guide marketing spend is SOM, and many plans never get that far.
- Using a global report for a UK-only business. A worldwide figure inflates every number below it.
- Double counting. Adding segments that overlap, such as “small businesses” and “businesses in London”, counts the same buyers twice.
- Treating the figure as fixed. Prices, regulation and competitors move. A market sized three years ago may no longer hold.
How to act on it
Start with SAM rather than TAM. Write down who your buyer is (a buyer persona helps), where they are and what they spend each year on what you sell. Find a countable source for the number of such buyers, multiply, and then sense-check the result against your current revenue. If you already hold a large share of your SAM, growth will come from widening the market rather than from more of the same advertising.
Then use the figures to set targets that hang together. A realistic SOM gives you a revenue goal, which gives you a sensible ceiling for customer acquisition cost and, from that, a budget. Revisit the numbers once a year alongside a fresh competitor analysis. If you want this turned into a written plan with a budget split, it is part of how I run digital marketing strategy and consulting.