Updated: 31 October 2026

Estimate your market size sensibly

This prompt helps you estimate the market for a product in a country or region from your customer type, price per customer per year and any data you have, using both a bottom-up and a top-down approach. Check the assumptions yourself.

text-market-size-estimate — chatgpt — 56 words

Help me estimate the market size for [PRODUCT] in [COUNTRY OR REGION].

Customer type: [WHO BUYS]
Price per customer per year: [PRICE]
What I know: [ANY DATA]

Do a bottom-up estimate (number of customers times price) and a top-down cross-check. List every assumption, give low, likely and high cases, and tell me which assumption matters most.

Edit in the builder Copy & open ChatGPT ↗Copy & open Gemini ↗Copy & open Claude ↗

Label every assumption clearly. Investors trust a transparent guess more than a huge number.

Get a better result

What you will get

A bottom-up estimate (customers times price), a top-down cross-check, every assumption listed, low, likely and high cases, and the assumption that matters most.

Why it works

Market size is an argument, not a fact, so the prompt asks for two methods and lists every assumption. The low, likely and high cases show the range honestly. As the tip says, a clear guess earns more trust than a big number, and knowing which assumption matters most tells you what to test.

Common mistake

The numbers look precise but are guesses.

Fix: Every figure should trace to an assumption. Ask for a sources column showing which ones came from your data.

Also watch for

The top-down number is huge and dominates. Trust the bottom-up figure more, since it is built from customers you can name.
The AI quotes market figures as fact. Treat any industry figure it gives as a lead to check against a real report.

Try a variation: first-year reach

Ask how many customers you could realistically reach in year one with your channels, and what share of the market that is.

Still not right? Reply with this

Show the bottom-up estimate as a table with each assumption on its own row, and tell me which two I should check first and how.