Advice > Consulting

21 market sizing questions with answers (McKinsey, BCG, etc.)

By Tom Parry on December 19, 2022 How we wrote this article
21 market sizing questions with answers

If you’re preparing for a case interview at McKinsey, BCG, Bain, or another top consulting firm, you can expect to face a market sizing question. This could be something like “What’s the market size for take-away coffee in this country?” or “How many bottles of wine are sold in the U.S. every year?” 

The best way to get the hang of these questions is to practise them. To save you hours of research, we’ve collected 21 typical market sizing questions with good quality solutions and listed them below.

Here’s an overview of what we’ll cover:

Click here to practise 1-on-1 with MBB ex-interviewers

1. What are market sizing questions?

Market sizing questions are typically asked at the beginning of consulting case interviews. They require you to perform rough calculations in order to estimate the size of a particular market without having any data available.

There are two types of market sizing questions. Most commonly, you'll be asked to estimate the value of a market - that is, to calculate its annual revenue. The market could be anything, from soft drinks to ping pong balls, and you’ll need to give an estimate of its annual worth (e.g £5 billion).

Alternatively, you may be asked to estimate the volume of a market - that is, to calculate the number of units sold (e.g 5 billion ping pong balls).

1.1 Why do companies ask market sizing questions?

Consulting firms tend to ask market sizing questions for two main reasons:

Firstly, it gives the interviewer the chance to see whether the candidate's basic mathematical and problem-solving skills are of a good standard, and whether they can use them quickly and logically in a pressure situation.

Secondly, consultants will often need to provide “guesstimates” and ball-park figures of market size while they’re talking to clients, be it on strategy cases or due diligence cases. Thus the ability to do a quick back of the envelope calculation, perhaps during or just before a client meeting, is of real practical value.

So, let’s take a look at some examples.

2. 21 market sizing questions and solutions

We’ve researched through the questions and solutions available online, and we’ve listed the best ones here for you, including links to video and written resources.

2.1 Medium-level questions

There's a whole list of examples below, but first let's work though an example together so that you can see how we recommend approaching a market sizing question.

2.1.1 How many t-shirts are purchased in New York City in a given year?

We always recommend using a 4-step framework.

Step 1: Ask clarification questions

Market sizing questions are usually ambiguous. Make sure you’re calculating the right numbers before you start. This also buys you some thinking time. You could ask:

  • “Does this include NYC only (8m) or the greater metropolitan area (20m)?" 
  • "Does 'shirts purchased' mean just in-store? Would an online purchase by someone in New York using a provider outside NYC count?"
  • "Does this include sportswear, or is it restricted to regular-use t-shirts?”

Let’s imagine that in this case, the interviewer says they’re interested in NYC only. They clarify that online purchases can be included as long as the buyer is in NYC at the time of purchase, and that sportswear should be excluded.

Step 2: Map out your calculations

We always recommend telling your interviewer your approach to the problem before you start making calculations.  You could lay out these five steps:

  1. Estimate the population of NYC.
  2. Estimate the number of t-shirts the average man in NYC buys each year.
  3. Estimate the number of t-shirts the average woman in NYC buys each year.
  4. Adjust estimates for age group differences.
  5. Find average and multiply by population of NYC.

Hopefully the interviewer is on board with your approach, so you can get started.

Step 3. Round numbers and calculate

Calculation step 1:
Estimate the population of NYC.

Let's imagine that you live in London. You know that London has about 8m inhabitants, and you think that NYC must be fairly similar.

Estimate: 8 million

New York is a fashion capital in a world of fast-fashion, and also a relatively wealthy city where people have disposable income for clothes shopping. These factors will push your estimates up.

Now, onto the trickier estimates. If you’re a man, start with men so you can use yourself as a base of reference. If you’re a woman, vice-versa. For argument's sake, let's say you're a man.

Calculation step 2:
Estimate the number of t-shirts the average man in NYC buys each year.

You can tell the interviewer that here you're using personal experience to make assumptions. Let's imagine that tees are your main item of clothing and you buy around 4 per year. You might say that you think this might be a bit under the NYC average, as you’re not interested in fashion and don’t have much time for shopping. Also, you want to count t-shirts given to men by someone else (their partners, for instance), and so this increases your estimate slightly.

Estimate: 5 t-shirts per year.

Calculation step 3.
Estimate the number of t-shirts the average woman in NYC buys each year.

Let's imagine that, drawing from personal experience, your perception is that women don’t wear t-shirts as often as men, but then again they tend to buy more clothes than men. You consider that they may also buy a lot of clothes for men, but as you've already mentioned, you counted these in the male estimate.

Estimate: 3 t-shirts per year.

Calculation step 4.
Adjust estimates for age group differences.

You may want to consider children differently, because children go through a lot of clothes as they grow, make a mess of them, etc. However, you could also factor in that children often wear a lot of passed-on clothing (from siblings, etc). You could conclude that these factors balance each other out, and so 3 for girls and 5 for boys seems about right to you.

Calculation step 5:
Find average and multiply by population of NYC.

Clearly, the average of 5 and 3 =  4.

4 x 8 million = 32 million.

Step 4. Sense check your results

Your calculations have been fairly simple, so there shouldn’t be any surprises. 32 million t-shirts sold per year in a population of 8 million? It seems reasonable.

You can give the interviewer your final answer:

Total number of t-shirts sold in NYC each year: 32 million

Now you've seen how to approach this type of question, have a go at the ones below.

2.1.2 Provide an estimate for the number of dentists currently working in the UK


2.1.3 Estimate the market size for sofas in the UK


How did you get on? We've listed some more helpful examples below.

2.1.4 More medium-level questions

Remember, there is often more than one valid way of approaching a market sizing question, so if your solution is different to the ones we've linked to, it doesn't necessarily mean it's wrong. However, it is worth learning an approach that works and sticking to it.


2.2 Hard questions

You can't predict how difficult your market sizing question will be, and so you should be prepared for it to be a little bit more complex. Let's apply our 4-step framework to a slightly trickier question.

2.2.1 Calculate the market size for weddings in the UK

Step 1: Ask clarification questions

Make sure of the actual number you need to calculate. You could ask the interviewer:

      • “Are we talking volume (number of weddings) or value (amount spent on weddings)?"
      • "If we’re talking value, do you want to take into account linked expenditure - stag and hen parties, engagement rings, etc - or are we just focusing on the cost of the actual wedding day itself?"
      • “Are we including guest expenditure, or just how much the wedding day costs the hosts?”

The interviewer tells you that they want the total direct spend on the wedding day, including guest spending at the venue. They’re not interested in related spend such as hen parties and guest transport, etc.

Right, now you’re ready for the next step.

Step 2: Map out your calculations

Here you could explain to the interviewer that you're going to do some segmentation. Why? Because although people can get married at any adult age, there is a huge difference in marriage rate between age groups.

To keep it simple, you could segment the population into age groups spanning 20 yo, and assume even population distribution across those. You can estimate the % of each segment to get married in a year, thus finding the total people getting married in the UK.

  1. Segment population and estimate % of each that will marry in a given year.
  2. Use % to calculate number of people estimated to marry in each segment, and add together to find total number of people marrying.
  3. Two people marry at each wedding, so we’ll halve the number of people marrying to find the number of weddings. 
  4. Estimate cost per wedding by estimating host spend and guest spend and adding together.
  5. Multiply total spend per wedding by the total number of weddings to find the market size.

You lay out this approach to the interviewer and hopefully they’re on board with it, so you can start calculating.

Step 3: Round numbers and calculate

Calculation step 1:
Segment population and estimate % of each that will marry in a given year

If you've memorised your cheat sheet, you know the UK population is roughly 70m. 

0-20 years - 17m (rounded from 17.5)

20-40 years- 17m

40-60 years - 17m

60-80+ years - 17m

You could tell the interviewer that you’re going to make some assumptions based on personal experience of living in the UK. (If you're from another country, base it on your own experience and adapt. E.g. if you're from the US you’ll decrease the percentages a little because you know that the UK is less religious than the US and therefore marriage rates should be lower.)

  • 0-20 years: Most of this age group is below the legal age of marriage and even at legal age, it’s fairly rare for people to get married before 20 in the UK. You might calculate that it’s less than 1 in 100 - let’s say 0.5%.

So, 17m /100 = 170k / 2 =  85k. You round this to 90k.

  • 20-40 years: You estimate that you have around 100 friends and relatives that you're on reasonably close terms with and probably just over half of these are in the 20-40 age group. You say that you tend to be invited to two weddings a year, with one of the newly weds coming from outside this pool:  you estimate that 3 people out of 60 in this age group marry each year -  that’s 5%. 

You already know that 0.5% is 90k. So you multiply by 10 to get to 5% =  900k.

  • 40-60 years: You estimate that weddings in this age group are around one third as common as the 20-40 segment, perhaps a little more due to second marriages. You call it 2%.

90k x 4 = 360k

  • 60-80 years: Probably not as rare as the first segment, given that all ages are applicable, but still fairly rare. You estimate 1%.

90k x 2 = 180k

Calculation step 2:
Use % to calculate the number of people estimated to marry in each segment, and add together to find total number of people marrying.

TOTAL: 90k + 900k + 360k + 180k = 1.530m people getting married. You round it to 1.5m

Calculation step 3:
Two people marry at each wedding, so you halve the number of people marrying to find the number of weddings. 

Divide 1.5m / 2  = 750k weddings per year.

Total number of weddings in the UK each year: 750k.

Calculation step 4:
Estimate cost per wedding by estimating host spend and guest spend and adding them together.

You could tell the interviewer that from what you’ve heard in the media, the average wedding in the UK costs the hosts £20k.

You need to add guest expenditure. Estimating 70 guests at each wedding, you estimate an average spend of £30. 70 x 30 = £2.1k per wedding, rounding it to £2k.

So, total direct costs of the average wedding comes to 22k.

Calculation step 5:
Multiply total spend per wedding by the total number of weddings = market size.

22k x 750k = 16.5 billion

Step four: Sense-check your results

It’s hard to have much sense of how many billions weddings should be worth. Instead, let’s check the calculation before that - the number of weddings in the UK:

750K weddings per year in a population of 70 million people, does that sound right?

Yes, it’s roughly 2% (1% doubled for the two people marrying) of the population marrying each year, which seems reasonable.

You confirm to the interviewer your estimate:

Total market size of weddings in the UK: £16.5billion

In fact, you’re a little over. The current market size for UK weddings is around $9 billion, with fewer weddings than you estimated. But the interviewer will be evaluating you more on the logic of the thought process than on how close your final result is to the real one. 

Right, let's take a look at some more questions.

2.2.2 Calculate the market size for medical consumables in GP practices (solution from 01'12)


2.2.3 Estimate how many women in the USA play golf


2.2.4 Calculate the adult disposable diaper market in the USA


2.2.5 More hard questions

  • How many petrol stations are there in the UK? (video solution from 06'16)
  • What’s the market size for residential light bulbs in the US? (written solution)
  • What is the total number of automobile tires sold in the US every year? (written solution)
  • What is the size of the sandwich market in India? (written solution, scroll down halfway)

The 21 questions we've included in this article should be a great resource for you when you need to practise market sizing questions. But what else should you be doing to prepare for them?  Let's take a look.


3. How to prepare for market sizing questions

The questions and calculations we’ve gone through here aren’t rocket science, but they require a calm head and can be tricky to pull off smoothly in a high-pressure situation. And of course, they’re even trickier if you’re not used to answering them!

However, if you prepare using the simple steps below, you should put yourself in a great position to crack them. Here we go:

3.1 Learn a framework

Having a framework will help you structure your answer logically and minimize your potential for mistakes. We recommend using the framework we laid out in the two solutions we walked you through above. See it in more detail in our ultimate guide to market sizing.

3.2 Memorise some basic data

Market sizing questions are not general knowledge or "lucky guess" tests, and you’re not expected to be able to quote all sorts of population demographics and industry stats.

That said, to make a good impression, we recommend brushing up on some basic facts such as the rough population of the country you’re interviewing in. In our ultimate guide to market sizing, we've put the most important data all together for you in a cheat sheet.

3.3 Practise on your own

Once you’ve learned the framework, we recommend answering lots of questions until the approach starts to come naturally. The question list in section 2 above is, as far as we can tell, the best resource available in terms of lists of questions and solutions.

We also recommend talking through your calculations out loud. This may sound strange, but it will help you be more methodical and will significantly improve the way you communicate your calculations during an interview.

3.4 Practise with experts

Of course, it's impossible to replicate a consulting case interview situation on your own. Practising with friends can really help, but if you really want the best possible preparation for personal experience interview questions, you'll also want to work with ex-consultants who have experience running interviews at McKinsey, Bain, BCG, etc.

If you know anyone who fits that description, fantastic! But for most of us, it's tough to find the right connections to make this happen. And it might also be difficult to practice multiple hours with that person unless you know them really well.

Here's the good news. We've already made the connections for you. We’ve created a coaching service where you can do mock interviews 1-on-1 with ex-interviewers from MBB firms. Learn more and start scheduling sessions today.


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