How should I size the TAM across multiple verticals for a B2B software tool?

[Lily72]

I’m trying to map out the market for a new B2B software tool we’re developing, but I’m stuck on how to accurately size the total addressable market when our product could serve several different verticals with very different adoption rates. My initial TAM estimate feels too broad to be useful for planning.

[Alexander18]

I tried to size the TAM by verticals and the top line just felt useless for planning. The numbers wandered a lot, so we pivoted to a bottom-up view per vertical and built a rough plan from counts of target accounts, typical deal size, and a few plausible win rates. It gave something actionable, even if it wasn't a clean market-size number.

[JonathanS]

Maybe the real friction isn't demand across verticals but getting into the right buying group. Are you sure the problem is market size rather than product-market fit in a narrow segment?

[OliviaYM]

We did a bottom-up mapping: for logistics, manufacturing, and healthcare we listed 120 target firms each, assumed a 75k annual contract, and used a 20% win rate to project yearly revenue. The numbers moved a lot when a single vertical dropped from 15% to 5% conversion, so the aggregate figure looked unstable but more grounded.

[JonathanS]

I drifted into a tangent once, counting all potential buyers in a sector, then realized the decision maker wasn't who signs off. It made me question whether the whole exercise is even the right problem to solve right now, or if we should run a few pilots first and wait to see where traction actually comes from.