Skip to Content

How to Answer Market Sizing Interview Questions: With Examples

Market sizing questions are the test of a consultant’s mettle. They are classic interview questions. In the case study interview, the interviewer is bound to ask you to make an estimate of a market size. Don’t be intimidated by market sizing. The numbers are big, but the logic can be simple!

Market sizing questions literally ask a candidate or consultant to estimate the volume or the value of a market for something. It tests peoples’ abilities to deal with a ball park figure, a 10,000 foot view and do a back of the envelope calculation.

When a consultant meets with a client to discuss the future of their airline for example, the consultant will do a market sizing to get a grasp on how big the broader market is. This will inform their strategy. Is their scope for expansion? How strong is the competition?

Market sizing questions test your mental maths, your business instincts and your ability to hold lots of information in your head. While balancing these concerns, lots of people end up with a solution that makes no sense or is intuitively too big/small. It is important to listen to yourself as you do this task to make sure you aren’t talking nonsense!

How to do market sizing?

There are two ways of doing a market sizing. It depends on the case.

1. Top-Down Market Sizing

The first and more common is a “top-down” calculation. You start by finding how many things there are in the market – the volume – and then zone in and narrow down your specific answer. i.e. You would do this if asked how many how big the market for bikes is in France. Whats the population of France – how many people cycle, etc.

2. Bottom-Up Market Sizing

The second is called “bottom-up”. This is much more common for guessing revenue or unit volume. i.e. You would use it for a question like, how much does my lemonade sell in a month.

  1. Start by unit price
  2. Then find the volume per day
  3. And then multiply it up.
Here is an example of market sizing in action from Kenton Kivestu.

3 Examples of Market Sizing Questions:

Interview examples that test market sizing include some of the following:

  • How many golf balls fit into an aeroplane?
  • How many traffic lights are there in London?
  • What is the size of the sandwich market in India?
Market sizing questions example

How To Answer Market Sizing Questions

To illustrate how to answer market sizing questions, we have unpacked the India example.

For this question, it is better to go from the top down. Like all interview questions or tasks in consultancy, ask questions at the start . Show that you can see the problems coming and make sure that you start off on the right line of thinking. This question is self-explanatory, but others might not be.

When you do your answer in an interview or real-life situation it is important to talk through your assumptions as you go. This makes it easy to follow what you are doing and it makes you look more impressive. Remember lots of people can do the maths, but to be a consultant, you need to have some level of linear/understandable way of thinking. It will also save you some embarrassment if you make an erroneous estimation. An interviewer is likely to jump in at this point if you are otherwise doing well!

  1. You should start by estimating India’s population. There are about 1.4 billion people living in India, but this is definitely something that would be acceptable to ask your interviewer.
  2. Then you want to figure out how many people have access to commercial sandwiches. You need an estimate of how many people live in urban centres. 20% would be a good estimate. 0.2 x 1.4 = 280. That makes 280 million Indians.
  3. But how many of these people can afford a sandwich or would choose to buy one? You should mention that India is a poorer country in GDP per capita, so maybe only 40% of people living in cities and towns have enough income for such a purpose. 0.4 x 280 = 112 You might want to round this to 11. Ask before doing so. Your interviewer will almost certainly accept a rounding to 112 million.
  4. So 112 million people are interested in buying sandwiches. But how often do they do that? This is the trickiest part of the question. You need to come up with sensible rules for when people buy sandwiches. To keep it simple, estimate that people buy a sandwich twice per week on their way to work. Therefore 2 x 52 = 104 sandwiches per year. 104 sandwiches x 112 million Indians = 11.6 billion sandwiches. This is the kind of calculation that you can reasonably be assumed to do without rounding. This is the volume of the market.
  5. Finally, you need an average unit price to multiply by your unit volume, to get a revenue. Let’s say a sandwich costs £2 in India. Therefore 2 x 11.6 = £23 billion industry.
  6. After sanity checking your result, it is wise to comment on the implications, even if you have not been asked. This is a big industry – what else would a consultant want to know? How does this inform their objective? Some consultancies call this the synthesis, so be aware if you are asked to synthesise!

If you enjoyed our content, subscribe here!


  • Will Bennett

    Will Bennett is a Cambridge graduate. He worked as a Consultant and Senior Consultant at Boston Consulting Group (BCG) in London. Will is the Founder of The Cambridge Consultant.