Joshua Franklin Wiedeman

TAM / SAM / SOM Market Sizing

TAM (Total Addressable Market), SAM (Serviceable Addressable Market), and SOM (Serviceable Obtainable Market) size a market at three levels of realism. TAM asks how big the whole market is. SAM asks how much of it you can serve today. SOM asks how much you can realistically win in the next 1 to 3 years.

How it works

The three tiers narrow like a funnel. TAM is total revenue if every possible customer bought a solution. SAM filters TAM by geography, product fit, price, and go-to-market model. SOM filters SAM by what you can win given your awareness, sales capacity, competitors, and growth. The final number is always an estimate. The real value is the assumptions, because they force you to be clear about who you sell to and why.

How to do it

  1. Calculate TAM top-down or bottom-up. Top-down: start from an analyst estimate of category revenue and adjust to your definition. Bottom-up: count potential customers with the problem you solve and multiply by your average annual contract value. Bottom-up is more credible because it uses your own numbers.
  2. Calculate SAM by filtering TAM. Apply the geographies, company sizes, industries, languages, and price points you actually serve. Example: global CRM is your TAM, but if you sell only to mid-market companies in North America, SAM is that slice.
  3. Calculate SOM from your realistic capture rate within SAM. Use current share, growth rate, sales capacity (reps times quota), marketing reach, win rate, and churn.
  4. Write down every assumption in a one-page table: the filter, the data source, and your confidence. People can then debate specific inputs instead of the final number.
  5. Update the model twice a year and assign an owner in strategy or product marketing.

What to measure

  • SAM-to-TAM ratio: SAM divided by TAM, showing how much of the market your current offer can address.
  • SOM capture rate: current revenue divided by SOM, showing remaining headroom.
  • Assumption sensitivity: change each assumption by a fixed amount (for example, 20%) and see which one moves SOM the most.

Best practices

  • Use bottom-up for SAM and SOM. Use top-down only as context for TAM, and explain any gap between the two.
  • Present low, mid, and high scenarios instead of a single number.
  • Tie SOM to the revenue plan. If the plan implies a large share of SOM, that is a specific claim the team can test.

Common pitfalls

  • Inflating TAM to impress investors. A disciplined, smaller TAM with clear logic is more convincing than a huge number that includes markets you will never enter.
  • Confusing TAM with SAM. Quoting a whole industry’s size when you sell a niche product to one segment in one region overstates the opportunity.
  • Building the model for a fundraise and never using it again. Use it for territory planning, segment priority, budget, and roadmap decisions.