Ace Market Sizing Interviews

How to Ace Market Sizing Interview Questions

Market sizing questions ("How many golf balls fit in a school bus?") test structured thinking and estimation under pressure. They appear in consulting (McKinsey, BCG), PM interviews (Google, Meta), and strategy roles. There is no "right answer" — interviewers evaluate your framework and reasoning.

The market sizing formula: start with a known anchor number (population, household count), then apply a chain of reasonable assumptions (% who do X × frequency × spending). Show your math clearly and sanity-check the final number.

Market Sizing Framework

1. Clarify — What market? What geography? What timeframe?
2. Choose an approach — Top-down (total addressable → narrow) or bottom-up (individual unit → multiply up)
3. State assumptions — "I'll assume the US has 330 million people..."
4. Do the math — Write each step. Round liberally (330M → 300M is fine)
5. Sanity check — "This implies $X per person, which seems reasonable because..."

For case studies: case study guide. For consulting: consulting interview guide.