Market sizing case questions are a core part of the consulting interview process.
For decades, leading consulting firms like McKinsey, BCG and Bain have used them to assess candidates quantitative abilities. In fact, they've been so effective that many tech companies have followed suit: it's not uncommon to get a market sizing question in product management or product marketing interviews at companies like Google.
In the beginning, firms asked hypothetical questions which exclusively tested a candidate's estimation skills.
It didn't matter if the situation was whimsical or had zero practical business implications. For example, a candidate might get the question: "Please estimate how many golf balls could you fit inside a 747 plane."
It's an interesting intellectual exercise. However, as an interview question, it has a crucial flaw: it doesn't truly test skills beyond pure quantitative ability. The solution: a true market sizing question!
Today, firms focus on a more sophisticated style of estimation question: the market sizing question.
These are estimation questions with added depth that tests the candidate's ability to pull in relevant knowledge and make reasonable assumptions about consumers, businesses and markets.
From the firm's perspective, this is a higher leverage type of question to ask because it simultaneously tests 1) quantitative skills 2) logical reasoning and 3) business acumen.
Let's look at a sample market sizing question for the rest of this discussion.
Your client, a leading pharmaceutical company, is planning to introduce a product to compete with Botox, which currently holds a near monopoly in its market. You would like to estimate the current size of the market in the US, which derives about half its revenues from cosmetic uses and half from therapeutic uses.
This particular question is focused on the healthcare industry but exhibits all the core traits of a market sizing question that could come up in any case interview! Below, let's apply a three-step approach to working through it.
For any market sizing question you face, whether the whole case is one giant market sizing question or you find a mini-market sizing exercise embedded within a large case, we recommend taking three steps:
Before jumping into any given market sizing question, it's important to lay out how you'll approach the drill.
You can take any market sizing task and break it down into a few key component parts. Then, you can work through each component independently and put all the parts together for the final answer.
For our sample question, sizing the US Botox market, we can start by organizing the key info. We know from the question that the cosmetic market is 50% of the total, thus if we can estimate the cosmetic market, we can easily scale up by 2X to estimate the full market size.
Next, if we zoom in on the US cosmetic market, we can define it as equal to the number of cosmetic customers multiplied by annual spend per customer.
Now that you've got a structure in place, you'll need to make assumptions and calculations to get to your total estimate.
Here, the key is to assume often and always round your numbers to make them easier to work with. Additionally, after you do any calculation, if the result is a messy number, you should round that number before you use it in a subsequent calculation.
At times, candidates avoid rounding because they think it will be impressive if they do incredibly precise math and get it right. A word of advice: avoid this trap like the plague.
It's a double whammy because:
Consultants pride themselves on simplifying messy problems. Thus, needlessly complicating a problem with messy numbers isn't going to win you points. In fact, it's counter productive.
Returning to our example, if we want to first calculate the number of US cosmetic customers, let's start by making some assumptions and rounding as needed:
With these nicely rounded assumptions, calculating the number of women in the relevant population is nice and clean: 300M people * 50% women * 50% relevant age * 20% use = 15M women.
Finally, after any series of calculations, it's helpful to sanity check your estimate and make sure it passes the smell test. While it's not necessary after every single calculation, sanity checking numbers after series of calculations, and of course, at the end of the exercise, is helpful.
For example, consider the calculation we just did above. If we were “off by a zero” which is a common error to make in a series of calculations, we might have ended up with 150M women. Given that 150M women would be all the women in the US (given a 300M population and 50% of the population is women), that would be a crazy result. It implies that *all* women in the US use Botox cosmetically. Smell test fail.
However, the current number of 15M is 5% of the overall population. While it might seem a little high, it feels plausible that some single digit percentage of the population might use Botox cosmetically.
As you go through a whole market sizing exercise, you'll essentially be repeating the steps above to work toward an overall estimate.
For the US Botox market, here is the step by step calculation one of our RocketBlocks Experts used to estimate the market. As you go through, pay special attention to the structured approach and the use of round numbers to simplify calculations. In addition, try to test yourself by periodically sanity checking a few numbers as well.
|Assumption||Population of US||300M|
|Assumption||Cosmetic use is almost exclusively women||50% women|
|Assumption||Population is evenly distributed between ages||Ages 0 to 80|
|Assumption||Relevant population is ages between||Ages 40 to 80|
|Calculation||Number of women in target market: 300M * 50% women * ((80 - 40) / 80)||75M|
|Assumption||Only used by the top X% of earners||20%|
|Calculation||Total annual cosmetic treatments for women: 1.5M + 375K||1.875M|
|Assumption||Average cost of a treatment||$200.00|
|Calculation||Size of cosmetic market for women: 1.875M * $200||$375M|
|Assumption||There is some small percentage of cosmetic market which is men (%)||5%|
|Calculation||Cosmetic Botox market for men and women: $375M / 95% of the market||Roughly 400M|
|Calculation||Total Botox market (cosmetic + therapeutic): $400M / 50% of market is cosmetic||$800M|
Thus, the final estimate is $800M.
A quick Google search turns up some market research which suggests the overall US market size is $1B and growing quicky (source data here). Not bad!
For another example, check out this video of me solving a market sizing question live.
In the video, we illustrate three different approaches to this question: a weak approach, an OK approach and a great approach. Finally, in the conclusion, we provide a compare and contrast and point out why the great answer really sets itself apart.
If you're looking for additional market sizing drills, RocketBlocks can help with that.
Our market sizing drills each come with a detailed answer like we walked through above, as well follow-up questions to further test your knowledge. You can sign up for a free trial today and give them a try.
Real interview drills. Sample answers from ex-McKinsey, BCG and Bain consultants. Plus technique overviews and premium 1-on-1 Expert coaching.