Discover · Core

Size the opportunity

Estimate how many people have the problem and what solving it is worth. A rough, honest number helps you compare this opportunity with others and decide how much to invest.

About 1-3 daysEvergreenLast reviewed 5 November 2026

Who this applies to

Skills it builds: Commercial and business senseData and measurement
PM types: All
Product types: All
Starting points: All
Ways of working: All
Experience: Intermediate (1 to 4 years)Experienced (5+ years)
Size of organisation: All

Steps, by experience

Beginner (under 1 year)

Decide what to count: users affected, time saved, revenue, cost avoided or risk reduced.
Start from the bottom up: how many people have the problem, how often, and what each occurrence costs or is worth.
Cross-check from the top down using market or organisation-wide figures.
Write down every assumption next to the number, with a source or a note that it is a guess.
Give a low, likely and high estimate rather than one number.
Compare the result with the cost of discovery and delivery so far.

Intermediate (1 to 4 years)

Choose the value measure that matters most to your organisation.
Build a bottom-up estimate and cross-check it top-down.
Show low, likely and high ranges with assumptions and sources.
Identify which assumption changes the answer most and plan to test it.

Experienced (5+ years)

Size the reachable segment you can realistically serve, not just the total market, and show how share grows over time.
Model value for users and for the business separately, including second-order effects.
Run a sensitivity check on the two or three biggest assumptions and present the range honestly.
Compare against other opportunities in the portfolio using the same method.

Who can do this

Owner: Product manager

Can be delegated to

Data Analyst or Performance Analyst: Find the counts and frequencies for the bottom-up estimate
Business Analyst: Gather cost, process and market figures for the cross-check

Reviewed by: Tech Lead, Policy / Legal / Compliance

Tool examples

Google Docs: Keep a short written explanation of the method alongside the numbers so others can follow it.
Power BI: Pull usage and volume data into a simple model with sliders for the key assumptions.
Looker: Build an explore that counts affected users by segment, so the estimate can be refreshed later.
Claude: Give it your assumptions and ask it to check the arithmetic and point out any assumption that looks too optimistic.

Definition of done

Bottom-up and top-down estimates, with a low, likely and high range
Every assumption listed with a source or marked as a guess
The most sensitive assumption identified

Common pitfalls

Quoting a huge total market that you could never reach
Hiding guesses inside precise-looking numbers
Sizing only the business value and ignoring user value

If you lead the team

What good looks like: Each opportunity has a rough, honest estimate of size and value, with the assumptions written down.