Market Sizing Interview Framework
This conversation was generated using Cook'd AI's career assistant and reviewed by Fallon Han from our editorial team for accuracy.
I am an MBA candidate in the UK targeting a strategy consulting associate role. I keep getting stuck on market sizing. How do I structure a strong answer so it sounds like real case logic, not just a rough guess?
Start with a clean frame, not a number. First, define the exact market and geography, then choose a sizing method that fits the question. For a consumer or B2B market, I usually break it into demand drivers: number of potential customers, purchase frequency, and spend per purchase. State your assumptions out loud, use round figures, and explain why they are reasonable. The key is to show logic before arithmetic. A strong answer often sounds like: segment the market, estimate each segment, sanity-check the result, then give a final range. That structure helps the interviewer see your thinking, even if the final estimate is imperfect.
What are the most common traps people fall into when they do market sizing in interviews?
The biggest traps are: being too vague about the market definition, double counting segments, and jumping into math before laying out the logic. Another common mistake is using too many precise figures, which can look fake and distract from the reasoning. Also, candidates often forget to check whether the result makes sense against a simple benchmark, like population size or industry spend. In consulting interviews, a neat estimate with clear assumptions beats a brittle, over-engineered one. If you realize an assumption is weak, say so and show how you would pressure-test it.
Can you walk me through the framework I should use if I am asked to size a market from scratch?
Yes. Use a top-down or bottom-up approach, then cross-check with the other one if time allows. Bottom-up is often easiest to explain: start with the relevant population, narrow to the addressable users, estimate penetration, then multiply by average annual spend or usage. For example, if you are sizing a professional service market, you might go from total firms to target firms to users per firm to spend per user. Top-down can work too if you start from GDP, category spend, or industry revenue and carve out the relevant slice. The best answers often combine both: one main estimate and one sanity check. That shows you understand both market logic and commercial realism.
How do I build assumptions without sounding random, especially if I do not know the exact data?
Anchor assumptions in something observable. Use UK population, household count, number of firms, or a familiar category benchmark. If you do not know the exact data, choose a simple round figure and explain the basis. For example, 'I will assume about half the population is relevant' is better than pretending to know an exact percentage. You can also infer from behavior: how often people buy, how many employees use the product, or how often firms renew a service. What matters is consistency. If one assumption implies another, make sure they align, because interviewers often test whether your chain of logic hangs together.
If I want to end with a clean final answer, what should I actually say to the interviewer?
Summarize the estimate in one sentence, then add the range and a brief caveat. For example: 'Based on my assumptions, I estimate the UK market at roughly GBP 300 million to GBP 400 million, with a central estimate of about GBP 350 million.' Then say what drives the number most, such as penetration or spend per user. That closing does two things: it shows confidence and signals you understand sensitivity. If there is time, mention the one assumption you would validate first in real life. That makes the answer sound commercially grounded, which is exactly what top consulting interviewers want.