Free calculator
Market Size Calculator
Four numbers in, TAM/SAM/SOM out. No signup, no email, and the maths is shown so you can defend it in a pitch.
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Market Size Calculator: what it does
TAM is every possible customer multiplied by what each pays per year, SAM is the slice you can actually reach with your product and geography, and SOM is the slice you can realistically win in three to five years. For most small companies SAM is 5–20% of TAM and SOM is 1–5% of SAM.
Last updated 3 August 2026
Worked example
Here's one we ran earlier.
40,000 independent UK salons · £348 a year each · 15% reachable · 3% winnable
TAM — £13,920,000
Total addressable40,000 salons × £348 a year. This is the whole market if every salon in the country bought from you and nobody else existed.
SAM — £2,088,000
Serviceable available15% of TAM. The UK-only, English-language, single-location salons your product actually fits today. 6,000 salons.
SOM — £62,640
Realistically obtainable3% of SAM. 180 paying salons in three to five years, which at £29/month is a real business for a two-person team but not a venture-scale one.
How it works
Three steps, no account.
Count the customers, not the dollars
Start with how many businesses or people have the problem. Trade associations, Companies House, census data and marketplace listings all give you a defensible number.
Cut it down to who you can serve
Remove everyone outside your geography, language, price band or product capability. What's left is your serviceable available market.
Be honest about your share
SOM is what you can win with the team and budget you have. Investors discount optimistic numbers, so a conservative SOM with clear reasoning is worth more than a big one.
Questions
Common questions.
What's the difference between TAM, SAM and SOM?
TAM is total addressable market: everyone with the problem, times annual spend. SAM is serviceable available market: the part your product and geography can actually serve. SOM is serviceable obtainable market: the part you can realistically win in three to five years.
How do I find the total number of potential customers?
Use a source you can cite. Companies House and the ONS in the UK, the Census Bureau's County Business Patterns in the US, trade association member counts, or the number of listings on a marketplace your customers use. Write the source down next to the number.
What's a realistic SOM percentage?
For an early company with no sales team, 1–3% of SAM over three to five years. Anything above 10% needs an explanation, such as a locked-in distribution partner or a market with only two other players.
Should I use top-down or bottom-up market sizing?
Bottom-up, if you can. Multiplying your realistic monthly customer additions by price and retention produces a number you can defend line by line. Use top-down as a sanity check that you haven't sized a market that doesn't exist.
Is this calculator really free?
Yes. It runs in your browser, nothing is sent anywhere, and there's no signup or email capture.
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