Bottom-up market sizing without a finance hire

You do not need a finance team to size a market. You need a clear buyer, a price, and a count you can source.

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Define who pays in one sentence. List the segments where that buyer shows up. Skip segments you cannot name or find in a public or licensed source.

Then count, price, and cross-check. Count accounts per segment. Apply a realistic attach rate. Multiply by your price. Put the sum beside a published market figure. If they disagree by a wide margin, fix the assumptions before you pitch.

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A four-step build

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1. Count accounts or people per segment from a source with a publisher and date. 2. Apply an attach rate you can defend. 3. Multiply by the price you actually charge. 4. Cross-check the total against a published aggregate.

Keep publisher, date, and link beside each figure. The path from claim to evidence should be short enough to answer in the room.

A memo built this way holds up in diligence because every line points somewhere. You keep the workbook. Assumptions stay editable.

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When the numbers disagree

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If the bottom-up total and the published figure diverge, treat that as a feature. It forces a clean look at segment counts, prices, and geography before a partner finds the gap first.

Founders without a finance hire often stop at a single TAM line. That is the number investors challenge first. A sourced segment table is slower to build and faster to defend.

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Where this sits in Brief

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Market sizing is the first deliverable. Model and Map build on it. If you are testing whether the idea has a market, start with Market. If you are raising soon, Model or Map adds the workbook and the investor path.

A market memo you built this way walks into diligence with a short answer ready: who buys, how many, at what price, and which source backs each line.