How to Calculate Market Size: the Formula, Five Steps and a Worked Example
Market size is what your buyers spend in one year: the number of buyers times purchases per buyer a year times the average price. You calculate it in three layers: TAM (everyone who could buy), SAM (the part your offer and location can serve) and SOM (the part you can win in your first year). Build the number bottom-up from buyers and prices, then check it against a top-down figure cut from a published industry total.
- Customers: the households or companies in the area you sell to that pay for what you offer.
- Purchases per customer a year: how often each one buys; a monthly membership counts as 12.
- Average price: what one purchase costs, in dollars.
Yearly market size = buyers × purchases per buyer a year × average price
Run it on your own inputs in the market size calculator; the result feeds one part of a market analysis.
The market size formula: volume, then value
Market volume = customers × purchases per customer a year. Volume is a count of transactions.
Market value = volume × average price. Value is the dollar figure people mean by market size.
Pick the price metric that matches how you charge: a monthly fee, a yearly contract value or an average order, counted over a year. Take the price from your price list or from competitors’ public prices. In our example, a family pays $19.90ex for a membership and buys 1ex a month, which makes 12 purchases and $238.80 a year.
Fix the period at one year, or the number cannot be compared with a competitor’s revenue or your plan. Lifetime value is a different number: it covers one customer’s whole relationship and belongs to unit economics.
TAM, SAM and SOM: the three layers
SAM stands for serviceable available market and SOM for serviceable obtainable market1.
| layer | what it counts | how you narrow it | in the example |
|---|---|---|---|
| TAM | everyone who could buy the category | a published industry total | $1.0bnex |
| SAM | the part your offer and location can serve | filters: geography, segment, price | $3.47 million |
| SOM | what you can win in year one | customers won × revenue per customer a year | $71,640 |
The last column shows our example, worked through below. The layers always hold SOM ≤ SAM ≤ TAM. If a layer comes out larger than the one above it, an input is wrong.
How to calculate market size in five steps
1. Define the customer, the unit and the period
Fix four things before you count:
- Who pays. For a children’s venue, the household pays, so you count households.
- Where. For a local business, the drive radius around the location.
- What they buy. The unit, such as one monthly membership.
- Over what period. One year.
For the profile itself, read how to find your target audience and build an ideal customer profile.
2. Count the potential customers
Public US data covers most counts:
- The Census Bureau’s County Business Patterns publishes the annual number of business establishments by industry (NAICS code) and county2, for business customers.
- The American Community Survey publishes household data by county, including households with children under 183.
- The Bureau of Labor Statistics’ Consumer Expenditure Survey publishes average annual household spending by category; the average for all consumer units in 2024 was $78,5354.
- Public companies’ annual reports (Form 10-K) are free on the SEC’s EDGAR database5.
Write the unit next to every count. Formula line: potential customers = units in the area × the share that fits your profile. In our example, the count is 15,000 households with children within a 20-minute drive, both figures assumptions.
3. Set the price and the frequency
Take the price from your price list or competitors’ prices, and the frequency from how people buy: a membership renews monthly, a birthday party happens once a year. If you have neither, ask likely buyers; the customer interview questions cover both.
Revenue per customer a year is the price times purchases a year; in our example, $19.90ex × 12 = $238.80.
4. Narrow to the market you can serve (SAM)
Apply each filter you can name, with one reason each:
- Drive radius: a local venue serves the families who can reach it.
- Segment: the offer fits families with young children.
- Price: the household can carry a monthly fee.
Formula line: SAM = TAM × the share left after each filter.
5. Estimate SOM and cross-check
SOM = customers you can win in year one × revenue per customer a year. The bottom-up SOM must fit inside the top-down SAM. Print SOM’s share of SAM next to it.
The number shows whether one location can fill its capacity and caps what you can spend to win a customer.
Top-down and bottom-up market sizing
Top-down: start from a published total
Take a published industry total and cut it down to your area with one share per cut, each with its reason. In the example by our method:
| layer | figure | cut | result |
|---|---|---|---|
| US industry, 2024 | $1.0bnex | start | $1.0bn |
| Utah | $1.0bn | × 1% (assumption) | $10.0 million |
| Salt Lake County | $10.0 million | × 34.7% of Utah’s residents | $3.47 million |
Salt Lake County had 1,216,274 residents on July 1, 20246, out of Utah’s 3,503,6137. The cut assumes spending follows population, so the result is a ceiling.
Bottom-up: count buyers and multiply
Bottom-up market size = buyers you can win × purchases a year × price
Bottom-up is the number you plan on. Its inputs are often assumptions too, so label each one as data (with its source) or as an assumption.
| method | start from | weak point |
|---|---|---|
| Top-down | a published industry total | the shares are estimates; a national total hides local demand |
| Bottom-up | buyers, frequency and price | each input can be an assumption |
Do both. If the bottom-up SOM exceeds the top-down SAM, one input is wrong.
SOM: how much you can win in year one
Market penetration rate = current customers ÷ potential customers × 1008. A new business has no customers yet, so its year-one rate is the share you assume.
A new, optional, local product starts at a low share. The share stays an assumption until a demand test shows real sign-ups.
Set the share from what competitors already hold. In the example by our method, the check found 1ex direct competitor, Kids Empire, with a 35%ex visibility share. Its top risk is that large families pick Kids Empire over a new venueex. That keeps our example’s first-year share at 2% (assumption). Run a competitor analysis before you pick yours.
See who already serves your market: check your idea for free
Worked example: a pretend-play town in a Salt Lake City suburb
The idea is a pretend-play mini town, sold to large families as monthly memberships, in a suburban Salt Lake City strip-mall unit: a kid-size grocery and vet clinic next to a fire stationex. Our idea check of October 15, 2026 rated it Worth buildingex with 70ex out of 100, from 15ex search queries and 32ex sources (example by our method). It found no measured search demandex, so the customer count is an assumption.
Utah has the largest average household size of any state: 3.04 persons per household against 2.57 nationally9. That is why the idea targets large families.
| layer | how | figure | label |
|---|---|---|---|
| TAM | published US industry total, 2024 | $1.0bnex | example by our method |
| SAM | $1.0bn × 1% × 34.7% | $3.47 million | Utah share assumed; county share from the Census |
| SOM | 15,000 households × 2% = 300 families × $238.80 | $71,640 a year | count and share assumed |
| Test | $71,640 ÷ $3.47 million | 2.1% of SAM | fits under the ceiling |
Each of the 300 member families pays $19.90ex a month, or $238.80 a year, so together they bring $71,640 a year. The bottom-up number is 2.1% of the SAM in our example, inside the top-down ceiling.
The market tells you how many families you can win; the unit economics tell you whether each one pays back. In the example by our method, LTV is $59.70ex against a CAC of $30ex, an LTV/CAC of 1.99ex, with payback in 5ex months. Work out yours in the unit economics calculator, and run these numbers in the market size calculator.
Five mistakes that break the number
- Mixing periods. A monthly fee times a yearly customer count without × 12 understates value twelvefold. Fix: write “a year” on every line.
- Calling the industry total your market. Fix: cut it to SAM with filters you can name.
- Counting the user instead of the payer. Fix: count households.
- Choosing the share to reach a revenue goal. Fix: set it from the competitors and test it.
- Using one method only. Fix: run both passes and check SOM ≤ SAM ≤ TAM.
FAQ
What is the formula for market size?
Customers × purchases per customer a year × average price. The result is one year of spending in dollars.
What is the difference between TAM, SAM and SOM?
TAM counts everyone who could buy. SAM is the part your offer and location can serve. SOM is what you can win in your first year.
Should I use top-down or bottom-up market sizing?
Use both. Plan on the bottom-up figure and treat the top-down figure as the ceiling it must fit under.
What share of the market can a new business capture?
Set the share from your direct competitors and your capacity, and mark it as an assumption until a demand test turns it into data.
How do I calculate market size with no data?
Start from Census and BLS counts plus your price list, label your one assumption, then carry the number into your plan: see how to write a business plan.
Sources
- salesforce.com, 09/03/2026
- census.gov, 06/26/2025
- census.gov, 11/24/2025
- bls.gov, 12/19/2025
- sec.gov, 10/02/2026
- census.gov, 07/01/2024
- census.gov, 07/01/2024
- getmonetizely.com, 06/21/2025
- mchb.tvisdata.hrsa.gov, 09/23/2026
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