TAM, SAM, SOM: How to Size a B2B Market (Worked Example With Census Data)

TAM is the revenue you'd earn if every possible customer bought from you, SAM is the part of that market your product and go-to-market can actually serve, and SOM is the share you can realistically win in the next one to three years. For B2B, the most defensible way to calculate all three is bottom-up: count the companies that fit your ideal customer profile, multiply by what one customer pays you per year, then narrow down.

Below, we work through a full example using real U.S. Census Bureau data, compare the conflicting rules of thumb you'll find online, and flag the common mistakes that make market-sizing slides fall apart.

The short answer

TAM (total addressable market): every potential customer × annual revenue per customer.
SAM (serviceable addressable market): the customers your product, geography and pricing can serve today × annual revenue per customer.
SOM (serviceable obtainable market): the customers your team can realistically win in a set period × annual revenue per customer.
For B2B: build all three from account counts, not from analyst headlines, and derive SOM from your sales capacity and win rate rather than a round percentage.

TAM, SAM and SOM at a glance

Layer	Question it answers	Bottom-up formula	Example (accounting software)
TAM	How big is the whole market?	All potential customers x annual revenue each	120,085 firms x $6,000 = $720.5M
SAM	What can we serve today?	Serviceable customers x annual revenue each	12,108 firms x $6,000 = $72.6M
SOM	What can we win in 1-3 years?	Customers we can win x annual revenue each	180 customers x $6,000 = $1.08M

You'll also see SAM written as "serviceable available market" and, on Slideworks' consulting templates, "service available market." The names vary, but the logic is the same: each layer sits inside the one above it.

Top-down vs bottom-up: why B2B should start at the bottom

There are two ways to size a market:

Top-down starts with a published industry figure and cuts it by geography, segment and share. It's fast, but every filter is an assumption, and the errors multiply.
Bottom-up starts with a single customer. You count the accounts that fit, attach what each pays per year, and add them up.

Bottom-up suits B2B because business markets are made of a countable number of companies. Hey Sid's September 2026 guide makes a useful point: a bottom-up model doubles as a target list, because the accounts you counted are the accounts sales can pursue. The former McKinsey and BCG consultants behind Slideworks also recommend bottom-up as the primary method, with clear segments and an explicit geography.

Use top-down as a cross-check. If both methods land in the same order of magnitude, you can be more confident. If they don't, one of your assumptions is wrong.

A worked example with real Census data

Say you sell practice-management software to U.S. accounting firms for $6,000 a year. The U.S. Census Bureau's Statistics of U.S. Businesses (SUSB), released in April 2025, counts firms by industry and employee size. Its 2022 data gives us everything we need.

Step 1: TAM. SUSB counts 120,085 employer firms in accounting, tax preparation, bookkeeping and payroll services (NAICS 5412). At $6,000 each:

TAM = 120,085 × $6,000 = $720.5 million a year

Step 2: SAM. Your product is built for teams, not solo practitioners, so you target firms with 10 to 99 employees. SUSB shows 12,108 firms in that band, while 88,381 of the 120,085 have fewer than five employees.

SAM = 12,108 × $6,000 = $72.6 million a year

Step 3: SOM. Base this on capacity, not a percentage. Suppose your team can work 900 qualified opportunities over three years and wins 20% of them. That's 180 customers.

SOM = 180 × $6,000 = $1.08 million in annual recurring revenue, about 1.5% of SAM

Worked example: TAM $720.5M from 120,085 US accounting firms, SAM $72.6M from 12,108 firms with 10-99 employees, SOM $1.08M from 180 customers won over three years — TAM, SAM and SOM for software sold to US accounting firms at $6,000 a year. Source: US Census Bureau SUSB 2022

Notice how much the numbers shrink. The SAM is a tenth of the TAM, and the SOM is about 1.5% of the SAM. That's normal. The SOM is the number your revenue plan, hiring and pipeline targets should be built on.

From SOM to a pipeline plan

A SOM only becomes useful when you turn it into activity targets. Work backward from the example above:

Customers needed: 180 over three years, or about 60 a year.
Opportunities needed: at a 20% win rate, 300 qualified opportunities a year.
Leads needed: if 10% of the accounts you contact become qualified opportunities, you need to reach about 3,000 accounts a year from a SAM of 12,108.
Coverage check: 3,000 a year is roughly a quarter of the SAM, so over three years you'd touch most of it. If the math requires contacting more accounts than exist, your SOM is too high.

This is the step most market-sizing guides skip, and it's where a bottom-up model earns its keep. The same account list that defines your SAM becomes the list your team prospects, and the conversion rates you assume can be checked against reality within a quarter. Replace the 10% and 20% assumptions with your own numbers as soon as you have them.

The top-down trap: confusing your customers' revenue with your market

The same Census table shows accounting firms took in about $215.7 billion in revenue in 2022. A common top-down shortcut would say: "If firms spend just 1% of revenue on software, the market is $2.16 billion."

That's three times our bottom-up TAM, and it isn't even our market. It includes every software category those firms buy, not just practice management.

Top-down shortcut of 1% of accounting firm revenue gives $2.16B, three times the bottom-up TAM of $720.5M and 30 times the SAM of $72.6M — A top-down shortcut can inflate the market several times over. Source: US Census Bureau SUSB 2022, Spona analysis

Some guides make this error explicitly. VantaInsights tells readers to use "total industry receipts" for their NAICS code as TAM. That works if you sell the industry's own product, such as opening a restaurant and sizing the restaurant market. It doesn't work if you sell into an industry, which is the case for almost every B2B vendor. Your customers' revenue tells you how big they are, not how much they'll spend with you.

What's a realistic SOM? The guidance conflicts

Search for SOM benchmarks and you'll find contradictory numbers:

Source	SOM guidance
LeadScraper (Jul 2026)	Most young companies capture 1-5% of SAM in three years
ICanPitch (Jan 2026)	3-5% of SAM by year five, though its own example reaches 53%
PulseAI (Apr 2026)	0.1-5% of SAM for early-stage businesses
Slideworks (Aug 2026)	For example, 5% in year one growing to 15% by year three
Foundation (Jul 2026)	Example assumes 10% of SAM in the initial years
Hey Sid (Sep 2026)	No universal figure; derive it from win rate and capacity

ICanPitch even contradicts itself. Its headline benchmark is 3–5% of SAM in three to five years, but its own worked HR software example ends at a year-five SOM equal to 53% of SAM.

The honest answer is that there is no standard percentage. Derive SOM from inputs you can defend:

Sales capacity: how many qualified opportunities your team can work in the period.
Win rate: your actual close rate, or a conservative estimate if you're pre-revenue.
Average contract value: from closed deals or your price list, not your biggest customer.
Competition: accounts locked into incumbents that you won't win this cycle.

PulseAI reduces the B2B version to a simple formula: sales reps × deals per rep × average deal value. If the percentage of SAM that falls out of that calculation looks strange, revisit the inputs rather than forcing a round number.

Where to find the numbers

For B2B bottom-up sizing, you need two inputs: an account count and a price. Good sources include:

Government business statistics: the Census Bureau's SUSB datasets count U.S. employer firms by industry and employee size, which is ideal for a first TAM. Note that they exclude businesses with no employees.
B2B data platforms: filter by industry, headcount, location and technology to count accounts that match your ideal customer profile. Our ICP template helps define those filters.
Your CRM: real closed-won contract values and win rates are the most reliable inputs you own.
Public competitors: Slideworks suggests reverse-engineering market size from a listed competitor's revenue and estimated share.
Analyst reports: useful as a top-down cross-check, as long as you cite the source and year.

For context, SUSB counted 6,395,635 U.S. employer firms in 2022, and 5,720,093 of them, about 89%, had fewer than 20 employees. If your product needs a larger team to pay off, your SAM shrinks fast.

TAM, SAM, SOM vs your ideal customer profile

These concepts overlap but aren't the same:

Ideal customer profile (ICP): the description of the companies most likely to buy and succeed with your product, such as "accounting firms with 10–99 employees in the U.S."
SAM: the ICP counted and multiplied by price. It turns a description into a number.
SOM: the part of that number your team can win in a defined period.

In practice, a sharper ICP produces a smaller but more credible SAM. If your ICP is vague, your SAM will be inflated, and every target built on it will be too.

Sizing markets outside the U.S.

The method is identical in any country: count the businesses that fit, then multiply by price. Most countries publish business counts by industry and size through their national statistics office or company register, and B2B data platforms can count matching companies across countries in one search. Keep currencies and years consistent when you combine countries, and size each country separately if pricing or product fit differs.

Five mistakes that break a market-sizing slide

1. Leading with a vanity TAM. "Healthcare is a multi-trillion-dollar market" tells investors nothing about your opportunity. LeadScraper's guide calls out the classic line: "we only need 1% of a billion-dollar market." Without a derivation, the percentage looks arbitrary.

2. Treating stated intent as conversion. Foundation's grocery-app example converts a survey result (15% say they would use the app) directly into SOM, producing a bottom-up SOM equal to 12% of SAM. Survey intent overstates real adoption, so discount it heavily.

3. Counting transaction volume as revenue. Marketplaces and payment businesses keep only their take rate. A 10% take rate means your market is one-tenth of the transaction volume, a point both ICanPitch and LeadScraper make.

4. Sizing a new market off the old one. In June 2014, NYU professor Aswath Damodaran valued Uber at $5.9 billion, against a $17 billion funding valuation, using a $100 billion global taxi and limo market and a 10% maximum share. Uber investor Bill Gurley replied that a much better product expands the market, citing McKinsey's 1980 forecast of 900,000 U.S. cell phone subscribers by 2000, against an actual 109 million. Box CEO Aaron Levie made the same point, as Startup Archive recounts, comparing it to sizing the car industry by counting horses in 1910. For most B2B products, the lesson is narrower: if you genuinely create new demand, say so and show evidence, rather than inflating the TAM.

5. Never updating the model. Pricing, ideal customer profile and geography all change. Recalculate at least yearly and before any fundraise, launch or market entry.

Claims that don't hold up

Claim	Where it appears	What the evidence shows
VCs need a $1B+ TAM for a Series A	ICanPitch (no source)	Sequoia's pitch guide sets no TAM threshold
TAM = total industry receipts for your NAICS code	VantaInsights	Only true if you sell the industry's own product; B2B vendors should count accounts x price
A realistic SOM is 3-5% of SAM	ICanPitch	Its own worked example reaches 53% of SAM
72% of new-product failures come from flawed demand assumptions	Zapulse (no source)	CB Insights: poor product-market fit cited in 43% of 431 failures
Top-down and bottom-up within 15% means solid assumptions	LeadScraper	No standard tolerance; others use "same order of magnitude" (Zapulse)

The investor-threshold claim is the most repeated. ICanPitch states VCs need a $1 billion-plus TAM for a Series A, but gives no source. Sequoia's own pitch guide asks founders to "identify your customer and your market" and notes that some of the best companies invent their own markets, with no TAM threshold attached.

Similarly, Zapulse states without a source that 72% of new-product failures trace to flawed demand assumptions. The best available data, a CB Insights analysis of 431 failed venture-backed startups published in March 2026, found poor product-market fit cited in 43% of failures. It's an important factor, but not the same claim.

How to present TAM, SAM and SOM

Show the derivation, not just the circles. One line of math under each number earns more trust than a polished graphic.
State the geography and year. "U.S. accounting firms, 2022 Census data" can be checked; "global market" can't.
Use ranges. Give conservative, base and aggressive SOM cases, and name the one or two inputs that move the result most.
Match SOM to your financial plan. If your year-three revenue target exceeds your SOM, one of them is wrong.
Keep the account list. A bottom-up SAM is also your prospect universe, and our guide to building a lead list covers turning it into one.

Here's how the accounting-software example might read on a single slide:

TAM: $720.5M. 120,085 U.S. accounting, tax and payroll firms × $6,000 a year (U.S. Census Bureau, 2022).
SAM: $72.6M. 12,108 firms with 10–99 employees, the segment the product is built for.
SOM: $1.1M ARR in three years. 900 qualified opportunities × 20% win rate = 180 customers.
Plan: year-three revenue target of $1.0M, inside the SOM, with two account executives.

Every line can be checked, and an investor who disagrees with an assumption can change it and see the effect. That's the real goal: a model people can argue with, rather than a number they have to take on faith.

Turn your SAM into real accounts with Spona

A bottom-up SAM is only as good as your account count. Spona shows you how many companies match your criteria before you buy a single lead, so the number on your slide comes from real records rather than a guess:

Market size analysis first: describe your ideal customer and see how many matching companies exist before you spend anything.
Chat to leads in about 4 minutes: Spona's AI mines 40+ data sources to build a verified, scored list of those accounts.
Per-lead pricing: free samples, no contracts, and bulk leads from about $0.01 each, so you can test a segment cheaply.
Verified data: Spona's AI cuts lead research time by 90% and states its leads are 95% accurate.
Proven results: Qonto saw an 80% higher connect rate and Zizr tripled its outbound demo bookings.

To see what each lead in your SOM is worth, try our lead value calculator.

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FAQ

What is TAM, SAM and SOM in simple terms?

TAM is the whole market if everyone bought from you. SAM is the part your product and reach can serve. SOM is the part you can realistically win in the next one to three years.

What is the formula for TAM, SAM and SOM?

For bottom-up sizing: TAM = all potential customers × annual revenue per customer. SAM = serviceable customers × annual revenue per customer. SOM = customers you can realistically win in the period × annual revenue per customer.

How do you calculate TAM for a B2B company?

Count the companies that fit your ideal customer profile, using government business statistics or a B2B data platform, then multiply by your average annual contract value. For example, 120,085 U.S. accounting firms × $6,000 = $720.5 million.

What is the difference between SAM and SOM?

SAM is the market you can serve with today's product, pricing and geography. SOM is the share of SAM you can actually win, given your sales capacity, win rate and competition.

What is a good SOM percentage?

There's no standard. Published guidance ranges from 0.1% to 15% of SAM depending on stage, and some examples go much higher. Derive SOM from your sales capacity and win rate instead of picking a percentage.

Should I use top-down or bottom-up market sizing?

Use bottom-up as your main method for B2B, because you can count real accounts. Use top-down as a cross-check, and investigate if the two differ by more than an order of magnitude.

Can TAM be smaller than you expect and still be a good market?

Yes. A $70 million SAM can support a profitable company with a few hundred customers. It may be too small for some venture investors, but for a bootstrapped business or a new product line it can be exactly right. Size the market honestly, then decide what kind of company it supports.

Is TAM measured in revenue or number of customers?

TAM is usually stated as annual revenue, but in B2B it should be built from a count of accounts. Show both: the number of companies and the revenue they represent at your price.