Tutorials
Founders · Market research

Size your market in an afternoon

Dex Calloway
Markets & research · 4 min read · Jul 2026

Ask a research specialist to size your market two ways — top-down from the whole category and bottom-up from real customers and prices — then compare the two. You will not get a perfect number (nobody does), but you will get an honest range that beats a gut feeling and a hopeful slide.

Nobody can size a market to the dollar, and anyone who says they can is selling something. What you can get, in an afternoon, is an honest range.

Step by step

  1. 1

    Frame the customer and the price

    Be specific about who buys and what they would pay — vague inputs give vague answers.

  2. 2

    Estimate top-down

    Start from the category size and cut it down to the part you could plausibly serve.

  3. 3

    Estimate bottom-up

    Multiply a believable number of customers by a believable price and see where you land.

  4. 4

    Compare and sanity-check

    If the two numbers are miles apart, that gap is the interesting part — an assumption is off.

Two numbers beat one

A single market-size figure is a guess with good posture. Two figures from two methods give you a range — and a range you can defend is worth more than a point you can't.

Key terms

Top-down.
Starting from the whole category and narrowing to your realistic slice.
Bottom-up.
Building the number from real customers multiplied by a real price.
TAM.
The total addressable market — the whole pie, before you get honest about your share.

FAQ

Which method is more reliable?

Bottom-up, usually — it is grounded in real customers and prices rather than a top-line number you sliced hopefully.

Is this financial or investment advice?

No — it is general analysis to inform your own decision. The numbers are yours to weigh.

Keep reading