A defensible market size is the difference between a thesis that survives the investment committee and one that dies there.
Top-down vs bottom-up sizing
Top-down sizing starts from a published industry number and applies a percentage. It is fast, cheap, and uncontested because it is uncontestable. Bottom-up sizing starts from segments, account counts, willingness-to-pay and attach rates, and assembles the market from the unit of the buyer up. The first is a slide. The second is a defensible argument.
Every Critical Deal market sizing engagement is bottom-up. We will use top-down numbers as sanity checks, but they are never the base case.
What we model
- Segment map. Every segment named, with its firmographic and behavioural definition.
- Account counts. Per segment, per geography, per maturity stage.
- Willingness-to-pay. Tested against actual buyer interviews, not benchmarked from comparable categories.
- Attach and adoption rates. What percentage of the segment is buying today, what the trajectory looks like, and how to read the leading indicators.
- Competitive share assumption. Realistic share to win inside the SOM window, with the assumptions named explicitly.
- Sensitivity. A range, not a point. Every assumption that moves the number by more than 5% gets its own sensitivity test.
What you get
- A TAM/SAM/SOM model built in the spreadsheet of your choice, shipped to you (not locked in our system).
- A source-trail document: every assumption mapped to a source, with the methodology shown.
- A sensitivity table showing the impact of every material assumption.
- A board-ready summary: the verdict, the size, the range, the confidence level.
- Buyer interview transcripts where willingness-to-pay or attach was tested.