How to calculate TAM bottom-up for a sales team
Count the companies that fit your segment before you buy a list: industry code, region, headcount, a sample of 25, and what the whole exercise costs.
A top-down market estimate can describe an industry without telling sales which companies to work. For quota planning, start with the companies that meet your own criteria, check which of them you can reach, and compare that count with what a rep can handle. Bottom-up TAM begins with the company count, not a percentage of a broad market report.
Top-down is for the deck, bottom-up is for the quota
Top-down starts with a market estimate and narrows it by assumed shares. Bottom-up starts with the customer: the number of companies that fit your segment, multiplied by what a customer pays you in a year. Check the company count carefully before buying a list; a larger list is not useful if most records fall outside the segment.
Describe the segment in filters a database understands
Write your actual target segment as one sentence first. Each part should become a filter a company database can apply: region, industry or NAICS code, headcount, revenue, growth or technologies. Industry labels differ between databases, so a count by industry name belongs to that database's taxonomy. Headcount is an estimate for many companies, which makes the edges of a size band uncertain.
NAICS in three minutes
NAICS is the industry classification of the United States, Canada and Mexico. A code gets more specific from left to right: sector 54 is professional, scientific and technical services, 541 is the subsector, 5415 is computer systems design and related services, 541511 is custom computer programming. For sales, the four-digit level is usually the right grain: specific enough to mean one kind of company, broad enough to leave a market.
The official numbers are public and free. The US Census Bureau's Statistics of US Businesses 2022 counts 127,147 employer firms in NAICS 5415; 115,692 of them have fewer than 20 employees, about 4,500 have 50 to 499, and about 1,060 have 500 or more. Those are payroll units without names or contacts. Compare a database count against the official scope before treating it as a market size; a large gap calls for a closer look at the filters and definitions.
Count first, buy nothing
In ListPlus the counting happens in Find, mode Markets. Filters on the left, one chart per property on the right: Region, Industry, NAICS code, Employees, Revenue, Company type and more, one bar per value with the number of companies behind it. Picking values, by clicking bars or adding filters, costs nothing. When the segment is complete, you click Calculate, which counts everything you picked in one step. One calculation costs 1 credit, $0.035 on Pro and $0.06 on Basic; a combination anyone calculated in the last hour costs nothing.
In the NAICS filter you open a sector and walk down level by level, or type a code or a word. The result shows the total and a breakdown by property. You can compare size bands without loading company records.
Tighten the count: exclusions and model companies
Two moves make the number honest. Leave values out: hover a bar and click the minus, and the filter reads "without companies of 1–10 employees" or "without agencies". Or add up to ten of your best customers under "Companies like these"; the count then shows companies similar to them, and every other filter narrows that group. Watch the "Not stated" line under the bars: revenue is known for a small share of companies, and a revenue filter drops every company without a value.
Load a sample of 25 before loading 1,000
A count is a claim until you look at the companies. Markets makes you load a sample first, 10, 25 or 50 companies, at 2.5, 6.25 or 12.5 credits. Read the 25 one by one: are they the kind of company you meant, is the headcount plausible, are there resellers or subsidiaries you did not want? Fix the filters and sample again. Only then load more, at 0.25 credits per company; 1,000 companies are 250 credits, $8.75 on Pro. One search hands over at most 1,000 companies, so a bigger segment is loaded in parts.
From there the loaded companies go into a company list with Add to list, and in the list you find the people at those companies: the TAM is companies, the pipeline is people. The count stays in the Find history, so a colleague can reopen it in the next planning round.
Calculate from the count you actually get
Use the result of your own filtered search. Multiply that count by the share of your sample that passed the check and by your actual annual contract value; then separate the firms your team can reach from those it cannot. ListPlus charges 1 credit per new filter calculation and 0.25 credits per company you load, with the sample charged at the same per-company rate. Your final cost and TAM follow from your own count rather than an assumed market size.
What replaced Clearbit's free TAM calculator
For years the quick answer to "how big is my segment" was Clearbit's free TAM calculator. After HubSpot's acquisition, Clearbit's free tools, the calculator among them, ended on April 30, 2025. What remains are the two sources above: the Census for the official count by NAICS, size and state, free but without names; and a company database for the count you can reach, with a sample to check it. The official number tells you whether the database count is plausible, the database count tells you how many accounts to plan for.