TAM
Total Addressable MarketTAM is the total revenue you'd earn if every possible customer on earth bought from you — the ceiling of the opportunity, not the plan.
TAM answers a single blunt question an investor asks in the first five minutes: if this works completely, is it big enough to matter? It's the whole pie before you carve out the slice you can actually reach. You can size it two ways. Top-down starts from an industry report ("the global X market is $300B") and is fast but easy to inflate. Bottom-up multiplies real units by real prices (number of customers × what each pays per year) and is harder to fake — which is exactly why investors trust it more.
The classic move is to reframe the market so it's bigger and truer at once. Uber didn't size "the taxi market." It sized "every trip a person takes in a city," which is an order of magnitude larger — and, as it turned out, more honest about what the product replaced.
Ride-hailing. TAM = all urban transportation spend (~$1T+). That's the headline that makes the opportunity look worth chasing. But nobody captures their TAM — the next two concepts exist precisely to shrink it down to something believable.
"We only need 1% of a $300B market." That sentence has killed more pitches than it has won. A 1%-of-a-giant hand-wave signals you haven't done the bottom-up math. Big TAM gets you a meeting; bottom-up SOM gets you a term sheet.
TAM sets the ceiling. If even a generous capture of the market can't sustain a real business, the idea is too small — or, more often, the market is defined too narrowly. Reframe before you shrink.