"How many coffee cups are sold in the US per day?"
Market sizing tests your structured thinking, ability to make reasonable assumptions, and comfort with ambiguity — core consulting skills.
State your approach before calculating — top-down or bottom-up.
Break the problem into components with clear assumptions.
Do the math out loud, rounding for simplicity.
Sanity check your answer against known benchmarks.
I will use a top-down approach. US population is about 330 million. Let me segment by age: roughly 250 million are adults (15+). I will estimate coffee drinking rates by segment: about 65% of adults drink coffee, so 162 million coffee drinkers. Average consumption: heavy drinkers (30%) average 3 cups, moderate (40%) average 1.5 cups, light (30%) average 0.5 cups. Weighted average: 0.3×3 + 0.4×1.5 + 0.3×0.5 = 0.9 + 0.6 + 0.15 = 1.65 cups per drinker per day. Total: 162M × 1.65 = about 267 million cups per day. Sanity check: the NCA reports about 400 million cups daily, so my estimate is in the right ballpark — I may have underestimated heavy drinkers.
Structure matters more than precision — interviewers watch your process.
State assumptions explicitly so the interviewer can challenge them.
Round aggressively — 330M not 331.9M. This is about logic not arithmetic.
Neither is inherently better. Top-down starts from population and segments down. Bottom-up starts from individual units and scales up. Using both to cross-check is ideal.
The process matters more than the answer. If your approach is logical and assumptions are stated clearly, being off by 2-3x is fine. Wildly off (10x) suggests flawed logic.
Practice daily with random questions: how many gas stations in your city, how many flights per day, revenue of a local restaurant. Build a library of base assumptions (population, household size, income).
HireMe AI listens to your interview in real-time, detects questions, and generates instant answer suggestions — so you never freeze up again.
Try HireMe AI Free