At what point is it appropriate to just ask for figures in a market sizing question?

Market sizing
Recent activity on Jan 28, 2019
3 Answers
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Geoffrey asked on Jan 27, 2019

Context: You have no idea how to size the particular problem because you have never interacted with said topic

Example: Estimate the weight of the Eiffel tower, by estimating the number of blocks the Eiffel tower takes up.

We know the tower is big, made of steel, can you just ask how tall it is? (explaining you would use the height and number of blocks it takes up in an effort to calculate the total mass and calculate that by the weight of the materials.

Similiarly, we know the population of the United States, but even as an American I wouldnt know how big the country is in area. Would it be professional to say all the facts you did know, but ask how big the area in question is?

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Anonymous A replied on Jan 27, 2019

You are not supposed to ask for any figures in market sizing questions.

You could say based on xyz, I'll assume that the area is this big. If you are way off, the interviewer may correct you. That's why the interviewer doesn't care about you being factually correct, he only cares about your logic. Use references, e.g., you know how tall the Rockfeller center is, and you know it's considered rather tall, hence you assume that Eiffel would be maybe 50% of that height. You can't just say I don't know, tell me. You must have seen the Eiffel tower hundresds of times on pictures.

To give you an example, you can calculate the area of USA by using the following assumption:

  • The airplane flight time from NYC to SF is about 5 hours
  • The plane speed is 600 miles/hour
  • USA is like a rectangular in the area. Vertically USA is about half of USA horizontally. The size of the rectangular is a*b, where b=a/2.
  • Calculation: USA area = a*a/2 = (5 hours * 600 miles/hour) * (5 hours * 600 miles/hour) / 2 = 3,000 * 3,000 / 2 = 4.5 million sq miles. The actual area is 3.8M. You are off by 18% here, that's totally reasonable.
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replied on Jan 28, 2019
McKinsey Senior EM & BCG Consultant | Interviewer at McK & BCG for 7 years | Coached 350+ candidates secure MBB offers

Hi Geoffrey,

well - I would recommend to just ask the interviewer at the beginning whether you are expected to make all assumptions yourself or whether he has some information to lean on. This way all is clear from the onset.

Cheers, Sidi

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Content Creator
replied on Jan 28, 2019
McKinsey / Accenture Alum / Got all BIG3 offers / Harvard Business School


If the interviewer knows the figures - he will give them to you. E.g. if you have to calculate some market in $ and you've calculated the volume - the interviewer might give you the price.

Most of the things however you need to calculate yourself. E.g. using the speed of the plane and time to calculate the are of the US. Or using the Area of some other country to calculate the area of the US. Etc.


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