Bottom-up market sizing
In short
Bottom-up market sizing is a method that builds a market estimate from the ground up. You count the companies you could sell to, estimate the annual revenue per customer, and multiply.
It contrasts with top-down sizing, which starts from a large industry figure and takes a percentage. Bottom-up numbers are usually easier to defend because each input can be checked against real accounts and real prices.
The basic formula
Market size = number of target accounts x average annual revenue per account.
Say a team sells to logistics companies with 200 to 2,000 employees. It finds 4,000 such companies in its target regions and expects an average contract of 20,000 per year. The estimate is 4,000 x 20,000 = 80 million. These numbers are only an example.
How to do it
1. Define the target customer precisely
Use your ideal customer profile: industry, size, region, and any must-have traits.
2. Count the accounts
Use a company database or search tool with the same filters. Remove those that match your negative ICP.
3. Estimate revenue per account
Use your own pricing and realistic deal sizes by segment, not list price for every account. Larger accounts may buy more seats or modules.
4. Sum by segment
Calculate each segment separately and add them. This shows which segments carry most of the value.
Bottom-up vs. top-down
- Bottom-up: Counts accounts and prices. More credible and tied to your sales plan.
- Top-down: Starts from industry reports and takes a share. Faster, but the assumptions are harder to verify.
Common mistakes
- Counting companies that cannot buy: Include only accounts that fit your ICP and can use the product.
- Using one average price: Pricing usually varies by size. Segment it.
- Ignoring data quality: Duplicate or outdated company records inflate counts.
- Confusing TAM with winnable revenue: The bottom-up total is the opportunity, not a forecast.
Bottom-up market sizing FAQs
How do you calculate bottom-up market size?
Count the number of companies that fit your target profile, estimate the average annual revenue each would pay, and multiply the two. Do this by segment if prices differ, then add the segments to get the total market size.
What is the difference between bottom-up and top-down market sizing?
Bottom-up builds the estimate from counted customers and prices. Top-down starts with a large industry figure and applies a percentage. Bottom-up is generally easier to verify, while top-down is faster but depends on broad assumptions.
Is bottom-up market sizing more accurate?
It is often more defensible because each input, such as account counts and prices, can be checked. Its accuracy still depends on how well you define the target customer and how clean your company data is.
What data do you need for bottom-up market sizing?
You need a filterable company dataset to count accounts by industry, size, and region, plus your own pricing, deal sizes, or contract values. Historical sales data helps you set realistic revenue per account.
