TAM vs SAM vs SOM for B2B go-to-market

TAM, SAM and SOM are three nested measures of market size. TAM (total addressable market) is everyone who could buy what you sell, SAM (serviceable addressable market) is the part of that you can serve today, and SOM (serviceable obtainable market) is the share you can realistically win in the next few years.

For a B2B company, the most useful way to calculate all three is bottom-up: count the accounts that fit, then multiply by what each one pays. Done that way, you end up with more than three numbers. Your SAM becomes a list of named companies that sales and marketing can work.

TAM vs SAM vs SOM: what each one means

Acme is the example company we use across these guides. The worked example below shows where each figure comes from.

TAM: total addressable market

Every company, and the buyers inside it, that fits your ideal customer profile and could buy what you sell. In revenue terms it's the number of those accounts multiplied by your average annual contract value. The what is TAM guide covers it in depth.

SAM: serviceable addressable market

The part of your TAM you can serve right now. It's narrowed by things you can't change this quarter: the regions you sell in, the languages you support, integrations or security requirements, and the company sizes where your price works. You'll also see it called the serviceable available market. It means the same thing.

SOM: serviceable obtainable market

The slice of your SAM you can win in a set period, usually three years, given your team, budget and competition. This is the number that should drive targets and hiring plans.

Top-down vs bottom-up market sizing

Top-down sizing starts from a published figure for a whole category and narrows it with percentages: the category is worth so many billions, your segment is a fifth of it, you can reach half of that. It's quick and it gives context. But every percentage is an assumption nobody can check, and at the end you have a number with no names behind it.

Bottom-up sizing starts from the accounts. Define who fits, count them, multiply by contract value. It takes longer because you have to find the companies, and that's the advantage. The assumptions are visible, anyone can check the count by opening the list, and the output is something sales can work.

Use top-down as a sanity check if you like. Plan from bottom-up.

How to calculate TAM, SAM and SOM bottom-up: a worked example

Acme sells software to B2B marketing teams. Its average customer pays $15,000 a year. Here's how it sizes its market in four steps.

Step 1: Count your TAM

Acme's ICP is B2B SaaS companies with 50–1,000 employees in North America and the EU, funded from Series A to C, that use HubSpot. The buyers are the VP or Head of Marketing, demand gen, RevOps and the CMO.

Counting every company that matches gives 18,240 companies, with 46,910 contacts in those buying roles, about 2.6 per company.

TAM = 18,240 × $15,000 = $273.6 million a year.

Step 2: Narrow it to your SAM

Now take out what Acme can't serve today. Its team sells to and supports customers in North America only, and Europe is planned for next year. Filtering the TAM to North America leaves 11,400 companies.

SAM = 11,400 × $15,000 = $171 million a year.

Region is the most common SAM filter. Others include languages, required integrations, security or data-residency requirements, and a minimum company size below which your price doesn't make sense to the buyer.

Step 3: Build your SOM from capacity

Don't pick a percentage. Build the SOM from the team you have.

Acme has four account executives. Each closes about 30 new customers a year, so the team wins 120 a year, or 360 over three years.

SOM = 360 × $15,000 = $5.4 million a year in new recurring revenue by year three, or about 3% of the accounts in its SAM.

Now run it backwards. If Acme wins one in five qualified opportunities, those 360 customers need 1,800 opportunities over three years. That's roughly 16% of the 11,400 accounts in its SAM, which means Acme has to get in front of a large share of its market to hit a modest-looking SOM.

Step 4: Check it against how buyers buy

Only a small share of your SAM is shopping in any given quarter. John Dawes of the Ehrenberg-Bass Institute estimates that up to 95% of firms are out of the market for a given product at any one time. And in the 6sense 2025 B2B Buyer Experience Report, the winning vendor was already on the buyer's day-one shortlist 95% of the time.

Put those together and your SOM depends on accounts knowing you before they come into the market. If your plan only works the accounts that are in-market today, your realistic SOM is probably smaller than the capacity math suggests.

How to turn your SAM into an account list

The bottom-up math has already done half the work: to count 11,400 companies, you had to find them. Here's how to finish the job so the list is usable.

1. Write your SAM criteria as filters. Industry, employee range, region, tech used and anything you exclude. "Fast-growing" won't filter. "50–1,000 employees" will. The guide to list fields explains which ones to use.
2. Pull every matching company and dedupe against your CRM. Tag current customers, open deals and recent losses, so nobody in a renewal gets a cold email from you.
3. Add the buyers. List each role in the buying group at every account. The ideal customer profile guide covers how to pick the roles.
4. Enrich and verify. Add a LinkedIn URL and a work email checked with a verifier for each contact, and a phone if your team cold calls.
5. Score and split. Rank accounts on fit and intent (account scoring explains how). Contacts at accounts showing buying intent now go to sales. The rest go to marketing to warm up.
6. Keep the rest of the TAM in the same list, tagged. Acme's European accounts stay in, marked for later, so expanding to Europe starts with a filter change instead of a new build.

Across its full TAM, Acme's list came to 46,910 contacts: 2,346 Sales-ready (5%) and 44,564 Marketing-ready. Filtering to North America gives the SAM view the team works this year.

You can build this yourself with a data tool and someone to run it, or have it built. AdsGTM maps the full TAM and delivers it to your CRM within 72 hours of a kickoff call. Here's how it works.

Mistakes that make TAM, SAM and SOM useless

Sizing the industry instead of your buyers. Total industry revenue includes spend you'll never compete for. Count the accounts that fit and multiply by what they'd pay you.

Mixing units. Keep companies, contacts and dollars separate, and label which one each number is.

A SOM with no plan behind it. If you can't say which reps will win which accounts, the SOM is a hope.

Stopping at the slide. If your SAM never becomes a list, the sizing work changed nothing about how you sell.