Oct 08, 2026 by Offer

Market sizing: how many coffees (Explained): Interview Answer Guide 2027

How many cups of coffee does a city drink per day? Take population × share of coffee drinkers × cups per day — e.g., 8 million × 60% × 1.5 ≈ 7.2 million cups. This market sizing interview question tests structured estimation: segment the population, state assumptions, multiply through, and sanity-check, rather than producing a 'correct' number.

What the Market Sizing Interview Question Tests

Whether you segment before multiplying: population → coffee drinkers → cups per day.
Whether assumptions are explicit and reasonable, not hidden inside the arithmetic.
Whether you sanity-check the result and can flex it if the interviewer changes an input.

How to Answer the Market Sizing Interview Question

Understand the three-layer anatomy of every market sizing answer:

Layer 1 — population. Start from a known anchor: a city's population, households, or businesses. Round aggressively (8M, not 8,336,817).
Layer 2 — penetration. What share engages? Segment if it helps: adults vs. children, urban vs. rural, weekday vs. weekend.
Layer 3 — frequency. How often per day/week/year does each user consume? Multiply through and convert units once, at the end.

Then triangulate: a quick bottom-up cross-check (cafés × cups per café) that lands in the same ballpark proves your structure is sound.

Sample answer: "I would segment the city's 8 million people into coffee drinkers — say 60% of adults — times 1.5 cups a day. That is roughly 7 million cups daily, and I would cross-check against café count times throughput."

Common Mistakes With the Market Sizing Interview Question

One giant leap: 'I think it's 10 million.' No segmentation, no assumptions, no credit.
Mixing units — per day vs. per year — halfway through the calculation.
Defending a shaky assumption instead of adjusting: interviewers change inputs to test flexibility, not to argue.

Market sizing is the highest-ROI skill to drill for consulting interviews: the structure is identical every time, so five practice questions make you look experienced. Candidates who segment cleanly pass; candidates who guess fail.

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FAQ

What is the standard market sizing structure?

Population × penetration × frequency (top-down), or build up from segments like households or stores (bottom-up). State assumptions, multiply, sanity-check.

Top-down or bottom-up — which is better?

Both are valid; top-down is faster for 'how many coffees' style questions. Use whichever gives cleaner segments, and mention the other as a cross-check.

How precise should the final number be?

One or two significant figures with a range. 'About 7 million cups a day' beats '7,234,118' — false precision signals you missed the point.

What if the interviewer changes an assumption?

Recompute quickly and cheerfully. That is the real test: they want to see structured flexibility, not attachment to your first number.

Preparing for OC&C Strategy Consultants's interview? Our 2027 OC&C Strategy Consultants Online Test Tutorials (One-Way Video Assessment and Mapped Test) has practice questions and answers — $79 one-time, instant download.