How to build a list of every company in your market (your TAM list)

Ask a founder how big their market is and you'll often get a number from a report: "a $4bn market". Ask them to name the 800 companies they could sell to next quarter and it gets quieter.

The second question is the useful one. Here's how to answer it.

Step 1: Describe your best customers, not your ideal ones

Take your five to ten best customers (the ones who pay on time, got results, and would buy again). For each, write down:

• Industry, as specifically as you can ("independent veterinary practices", not "healthcare")
• Headcount band
• Country or region
• Who bought from you, by job title
• Anything else they share: a technology they use, a growth stage, a trigger event

The pattern you find is your filter. It's often narrower than you expected, and that's good. Our free ICP builder walks through this.

Step 2: Count it

Before you build anything, find out how many companies match. Company databases, LinkedIn Sales Navigator, industry registers and trade association directories all give counts. If the count is 40, your filter is too tight or your market is a list of named accounts (which is fine, but it's a different motion). If it's 400,000, it's too loose.

Step 3: Size it honestly

Multiply the count by what a customer is realistically worth per year. That's your market in money. Then be honest about how many of them you can actually reach and serve with the team you have. That smaller number is what you plan against.

Matching companies:          2,400
Average annual value:        $6,000
Full market:                 $14.4m a year
Reachable this year (25%):   600 companies
Realistic win rate (3%):     18 new customers
Revenue from new logos:      $108k

Plain arithmetic like this tells you whether your plan works before you spend on it.

Step 4: Split it into tiers

Tier	Share	How you work it
A	Top 5 to 10%	Researched by hand, several contacts, personal outreach
B	Next 20 to 30%	Light personalisation, sequenced email and LinkedIn
C	The rest	Content, ads, low-touch email

Tier A is usually the companies that look most like your best current customers.

Step 5: Put people on it

A list of companies doesn't reply to emails. For each company, add the one to three people who'd buy (our post on finding the decision maker covers who). Now you have a market you can actually work.

A worked example

A bookkeeping firm finds its best clients are UK restaurant groups with two to ten sites. The count is about 1,900 groups. Tier A: 150 groups in their home region, owners contacted by hand. Tier B: 500 elsewhere in England, emailed by operations director. Tier C: the rest, reached through a guide on restaurant VAT. Suddenly a vague "hospitality market" is a work plan.

Questions people ask

What is a TAM list?

A list of every company that fits your ideal customer definition, rather than a single market-size number.

How big should my market list be?

It depends on price. High-ticket services might have a few hundred targets; low-cost software, tens of thousands.

How often should I refresh it?

Every six to twelve months.