Bottom-Up Market Sizer

Free tool by AAJ - a market size you can defend, built from accounts you can count

Most market sizes start from an analyst figure and take a small percentage of it. The number is large and nobody can say which companies it is made of. This tool builds the size the other way: from segments you could actually pull as a list, the share of each that fits your ideal customer profile, the share your channels can reach, and what one account pays per year. It runs in the browser, so nothing entered is sent anywhere.

Use the tool at aajconsult.com/tools/bottom-up-market-sizer.

TAM, SAM and SOM

TAM is every account in the named segments multiplied by annual contract value. SAM keeps only the accounts that fit and can be reached. SOM is what the team can win in a year, worked out from capacity - sales reps and deals per rep, pipeline and win rate, or signups and paid conversion - and capped at SAM. It is never taken as a percentage of the market.

If a plan claims a share of SAM, the tool shows how many wins that share needs against how many the current capacity delivers.

Every link needs a source

Each account count, fit share and reach share can carry its source. The tool reports every one that has none rather than refusing to run, and names the assumption to verify first: the unsourced input sitting under the largest share of SAM. It also flags pricing marked as aspirational, because sizing on a price nobody pays yet inflates every number after it.

A top-down figure can be entered as a cross-check with its source. When it differs from the bottom-up TAM by more than three times - a threshold that is a rule of this tool, not an industry benchmark - the tool reports a likely definition mismatch instead of averaging the two.

Run this in your agent

The free AAJ agent skill Market Sizing does this job inside a coding agent, on your own data. Install it with npx skills add sarojkjha/aaj-marketing-skills --skill market-sizing.

Using Claude or ChatGPT instead? Add the AAJ engines as a custom connector, with no install: https://aaj-engines-mcp.sarojkjha10.workers.dev/mcp

Frequently asked questions

My honest number is small. What now?

That is the finding. If SOM is small against SAM, the constraint is capacity. If SAM is small against TAM, the constraint is fit or reach, and the answer is usually a second segment or a new channel.

Is my data stored or shared?

No. Everything runs in the browser and nothing is saved.

Related resources

ICP Fit Scorer - Pricing & ARPU Modeler - 90-Day Growth Playbook - Go-to-Market & Growth Planning hub - All free tools

A defensible number is the start of a plan.

Whether the constraint is capacity, fit or reach decides what comes next. See the Growth Audit.