Market Sizing Cases

This lesson teaches how to solve full market sizing prompts from start to finish.

Why This Matters

Market sizing cases test whether you can:

• structure an ambiguous problem quickly
• make reasonable assumptions
• calculate cleanly
• communicate a clear answer with confidence

They often reveal whether a candidate can stay logical without complete information.

The Case Pattern

A market sizing case is not just about the number.

It is about building a defensible path to the number.

Strong candidates choose an approach, state assumptions clearly, calculate step by step, and sense-check the result.

What the Interviewer Is Testing

When given a market sizing prompt, decide early whether to use:

• top-down logic
• bottom-up logic

Then break the estimate into manageable components and explain your assumptions as you go.

How to Approach It

1. Clarify the scope

Confirm:

• geography
• time period
• unit of measure
• customer segment if relevant

2. Choose the approach

Top-down starts from a larger population or market and narrows.

Bottom-up starts from units, locations, or behaviors and builds upward.

3. Break the problem into drivers

For example:

• population
• penetration
• frequency
• average purchase size

4. Make reasonable assumptions

Use assumptions that are:

• simple
• explicit
• internally consistent

5. Calculate and sense-check

After reaching a number, ask:

• does this seem realistic?
• what assumption matters most?

Case Example

Prompt:

"Estimate annual bubble tea demand in a city."

A strong candidate might choose a bottom-up approach:

• city population
• percentage of likely bubble tea consumers
• average purchase frequency
• average cups per purchase

Then they would multiply through and sense-check against the number of stores in the city.

What Strong Candidates Do

A strong candidate:

• clarifies scope before calculating
• chooses an approach deliberately
• states assumptions cleanly
• calculates step by step
• sense-checks the final result

What Weaker Candidates Tend to Do

A weaker candidate often:

• starts calculating without defining the market
• uses too many assumptions at once
• loses the arithmetic thread
• gives a final number with no sanity check

Common Traps

Mistake 1: Choosing an overcomplicated path

Simple logic is usually better than a clever but unstable chain.

Mistake 2: Hiding assumptions

Interviewers need to hear the reasoning, not just the output.

Mistake 3: Skipping the sanity check

An estimate that is directionally absurd will hurt credibility.

Practice Prompt

How would you estimate the annual demand for coworking seats in a mid-sized city?

Example Approach

"I would first clarify whether we want annual revenue, annual users, or annual units consumed, and define the geography clearly. Then I’d choose either a top-down or bottom-up approach depending on which seems more stable. For a consumer product, I would likely size the relevant population, estimate the share that purchases, multiply by purchase frequency, and then sense-check the result against real-world capacity or usage patterns."

What to Remember

• Market sizing cases test structured estimation, not just arithmetic.
• Clarify scope before choosing the approach.
• Keep assumptions simple and explicit.
• Always sense-check the final answer.