What is Total addressable market (TAM)?
Total addressable market is the full number of potential customers, or the revenue they represent, for a product if it reached every one of them.
Also called: TAM, market size.
For selling to local businesses, TAM is easiest to state as a count: how many establishments of a given trade exist in the places you can serve. Multiply by what one customer is worth per year to turn it into revenue.
The official source for that count in the US is the Census Bureau's County Business Patterns, which publishes establishments by industry (NAICS code) and geography. It counts establishments with paid employees, so sole proprietors without staff are outside it; a trade full of one-person operators is larger than CBP shows.
TAM is a ceiling, not a forecast. The serviceable part is the slice your product fits and can reach: the right trades, in your region, with a reachable contact. Coverage in any vendor's database is smaller again, and it is not market size: a page saying a vendor lists 600 dentists in a state is not saying the state has 600 dentists.
The market size calculator takes a trade, a place, your monthly price and a close rate, and gives the businesses 67Leads holds there, how many you can email, and the yearly market they represent.