Estimation Questions for Product Managers (How-to Guide + Examples)

Estimation or guesstimate questions are common in product manager (PM) interviews at companies like Google, Meta, and Amazon. 

Here are a few examples of PM estimation or guesstimate interview questions:

• What is the market size for driverless cars in 2025?
• What is the storage space required to host all images on Google Street View?
• What is the required internet bandwidth for an average college campus?
• How many kindergarten teachers are there in the US?
• What is the weight of a school bus?

Note that the above examples are real interview questions that were reported by PM candidates on Glassdoor.

Guesstimate questions can be really intimidating because they often cover huge topics with a lot of variables.

The good news is that they're fairly easy to answer if you know how to approach them. So let's walk through our 4-step process for solving them, as well as a few examples and shortcuts.

• How to answer estimation questions
• Example with answer: YouTube's daily revenue
• Cheat sheet
• List of practice questions
• How to practice estimation questions

Click here to practice 1-on-1 with FAANG ex-interviewers

1. How to answer product manager estimation questions ↑

We recommend using a four-step approach to answer guesstimate questions. Let's discuss each step one by one.

1. Ask clarification questions.
2. Map out your calculations.
3. Round numbers and calculate.
4. Sense-check your results.

Step one: Ask clarification questions

The first thing you should do is ask a few clarification questions to make sure that you know exactly what number you need to calculate.

For instance, let's imagine your interviewer asks: "How much money is spent on gas in the US every year?" Here are a few important clarification questions you would need to ask:

• Should we focus on gas consumption from road transportation only? Or also include home heating, air transportation, etc.?
• Should we focus on personal cars only? Or include consumption from commercial vehicles, too?

These questions are useful to make sure that you calculate exactly what your interviewer wants. In addition, they are also a great way to buy yourself some time. While your conscious brain asks these questions, your subconscious brain can start working on step two of the approach.

Step two: Map out your calculations

Once you know exactly what number you want to calculate, you then need to map the calculation steps to get to that number. Let's imagine we want to calculate the quantity of gas consumed by personal cars in the US.

Here is a step-by-step approach that you could use to get to that number:

1. Calculate the number of personal cars in the US.
2. Calculate the consumption of an average personal car.
3. Calculate the total consumption in gallons and then dollars.

If you struggle to find a starting point, an alternative approach is to begin from the number you want to calculate. Then, draw an issue tree from left to right, and calculate from right to left, as we have below. In addition, the advantage of this approach is that it will force you to be mutually exclusive and collectively exhaustive (MECE).

Both approaches are equally acceptable. But in both cases, you should validate your approach with your interviewer by telling them the different calculation steps you are going to take before starting to calculate numbers (in step three). This is important because it gives your interviewer a chance to rectify your course of action if they had another plan in mind.

Skipping this validation step is extremely risky because your interviewer might realize too late in the exercise that you are approaching the problem in a different way to what they wanted. In our experience, it's almost impossible to recover from that situation.

Step three: Round numbers and calculate

Once you've agreed on an approach, it's time to start calculating. You will need various data points (e.g. number of miles driven by an average US driver each year) to get to your final estimate. In most cases, your interviewer will ask you to make your own assumptions to get to the final number. But in some other cases, they might share data with you.

When making assumptions, it is vital that you pick simple numbers. For instance, you should use 350 days in a year instead of 365. You should assume that the average cost per gallon of gas is $3.00 instead of $3.05. Rounding numbers will make your calculations easier and decrease your likelihood of making a mistake.

In addition, you should talk out loud when doing calculations so that your interviewer can follow your thought process. Your interviewer is interested in what's going on in your head - not the final result.

Note: if you are looking for ways to become faster at mental math calculations, we recommend reading our interview maths guide.

Step four: Sense-check your results

Most candidates stop talking at the end of step three. They look up and expect their interviewer to tell them if they got to the right result or not. This is a mistake. The best candidates sense-check their results and try to spot their own mistakes before telling their interviewer they are done.

Mental calculation errors happen frequently. If your interviewer spots a mistake in your calculations, this will definitely play against you. But if you spot your own mistake, you still have a chance.

Now that you know what technique to use to answer guesstimate questions let's apply it to an example.

2. Example - Estimate YouTube's daily revenue ↑

Try answering the question below accurately and as fast as possible.

Try this question:

Answer:

1. Ask clarification questions

Here are some clarification questions that immediately come to mind for this guesstimate question:

• Do we want to calculate all of YouTube's revenues? Or just from advertising, which is likely to be the main source?
• Does YouTube charge advertisers per 1,000 views or per click? Are we interested in YouTube's revenues globally or just the US?
• Do we include YouTube Music?

Let's assume here that we want to calculate the advertising revenues ($) made by YouTube videos (ie. not music) in the US only. And let's also assume that YouTube mainly charges advertisers per 1,000 views for simplicity.

2. Map out your calculations

We could estimate YouTube's daily revenues in the US by taking a three-step approach.

1. Calculate the number of daily US YouTube users
2. Calculate the number of advertising videos they view
3. Calculate the corresponding revenue

In a real interview, you would need to lay out that approach to your interviewer and check that it works for them before starting your calculations.

3. Round numbers and calculate

Let's step through our approach:

1. Calculate the number of daily US YouTube users

• There are ~300m people in the US. Let's assume that the average life expectancy is 80 years old and that the population is equally distributed across each age.
• We now need to guesstimate how frequently each age group watches YouTube:
  • 0 to 9 y.o.: does not watch
  • 10 to 20 y.o.: 75% of days
  • 21 to 40 y.o.: 75% of days
  • 41 to 60 y.o.: 50% of days
  • 61 to 80 y.o.: 10% of days

In an actual interview, it's a great idea to justify the assumptions you make by relating them to your personal experience. For instance here you could say, "I'm going to assume that the 10 to 20 y.o. group watches YouTube 75% of days as my niece watches YouTube Shorts with about that regularity." And I'll assume 10% for the 60 to 80 y.o. group, as some older people do watch but my grandparents aren't even sure what YouTube is."

• We then need to calculate the number of users for each age group. We can divide the population into bands of 10 years by dividing 300m by 8: 40m. (or close enough). So we can say that our age groups spanning 10 years have 40m people, and the ones spanning 20 have 80m.
• We can then calculate the daily users in each age group (rounding up where necessary).
  • 0 to 9 y.o.: 0
  • 10 to 20 y.o.: 75% of days x  ~40m = ~30m
  • 21 to 40 y.o.: 75% x ~80m = ~60m
  • 41 to 60 y.o.: 50% x ~80m = ~40m
  • 61 to 80 y.o.: 10% x ~80m = ~10m
  • Total = 30 + 60 + 40 + 8 = ~140m
• The number of daily YouTube users is therefore approximately 150m in the US (round it to an easy number to help with the next stage of calculations).

2. Calculate the total number of advertising videos viewed

Let's now estimate the total number of ad views per day on YouTube.

• The number of videos viewed by users probably varies quite dramatically. Viewers who watch Shorts on their phone may easily view 20+ short videos per day, though most of these won't have ads.  Other users might just watch a single, long-form video. So, let's assume the average is ten videos per day. We've got 150m users, so that's 1.5bn views per day.
• YouTube does not systematically play an ad at the beginning of a video. Based on our experience, let's assume only 50% of videos viewed start with an ad. So, that's 0.75bn advertising video views per day.

3. Calculate the corresponding revenue

• Assuming YouTube charges advertisers $10 per 1,000 views, the total revenues it generates in a day is: 0.75bn x $10 / = $7.5bn, then divided by 1,000 = 7.5m

We therefore estimate that YouTube generates about $7.5m per day in ad revenues in the US only.

4. Sense-check your results

As mentioned above, it is crucial that you spend some time sense-checking your results. In practice, you should check your intermediate results as you progress through the estimation and your final result at the end. But here we are checking all the numbers in one place so it's easier for you to keep track of what we are doing.

• Intermediate result: If ~150m people watch YouTube every day, this means about half the country watches at least a video on any given day. That sounds reasonable.
• Final result: Similarly, if YouTube generates $7.5m per day, that means it generates ~$350bn per year. Does that sound possible? Here some familiarity of the tech industry and its revenues is needed. This is indeed a realistic sum, given Google said that YouTube made about $80bn in ad revenue across all geographies in Q1 of 2024.
• Remember that the interviewer is less interested in you getting the "right" answer, and more focused on how you structure your thinking and calculations. But if you end up with a number that seems way off, say so.

2.1 Example - Estimate time stopped at stop lights

Now you've learned how to use a framework, watch the mock interview below to see it in action. We recommend pausing the video at regular intervals so you can come up with your own answers.

Note: it's a good idea to learn some numbers for estimation questions such as the average cost per thousand views in advertising across all industries ($14.90) or Meta's ad revenues in early 2024 ($39bn). We've put together a cheat sheet later in this article to get you started with this.

3. Estimation questions cheat sheet ↑

At this stage, we feel it will also be useful for you to memorise some common assumptions, such as population and life expectancy, as they will often come up in estimation questions.

We've created a cheat sheet with socio-economic data, advertising data, and some company information below. You can download the slides by simply clicking this link: estimation questions cheat sheet

4. List of practice questions ↑

Here is a list of guesstimate questions that were asked in PM interviews at Google according to data from Glassdoor.com. Some include solution links to videos on how to answer them. These are great examples of the questions you may encounter in your interviews. 

If you'd like to learn about the other types of questions you may face, you can also visit our ultimate guide to product manager interview questions.

Now that you have a list of sample questions to work with, it’s important to consider how you will practice with these questions.

5. How to practice estimation questions ↑

With a lot to cover, it’s best to take a systematic approach to make the most of your practice time. 

Below you’ll find links to free resources and four introductory steps that you can take to prepare for estimation questions.

5.1 Study the company you're applying to

Get acquainted with the company you’ve applied to. In many cases, the product questions you’ll be presented with will be based on real-life cases the company is facing. If you’re applying to a specific team, study up on their products, the user, etc.

Take the time to find out which products you’ll most likely be working with, based on the job description, and research them. Look up relevant press releases, product descriptions, product reviews, and other resources in order to discuss what’s most important to the role: the company’s product.

If you'd like to learn more about a specific company's PM interviews, then we'd encourage you to check out our guide for that company below :

• Google product manager interview guide
• Facebook product manager interview guide
• Amazon product manager interview guide
• Microsoft product manager interview guide
• LinkedIn product manager interview guide
• Uber product manager interview guide
• Stripe product manager interview guide
• Lyft product manager interview guide
• Apple product manager interview guide
• TikTok product manager interview guide
• Coinbase product manager interview guide
• Airbnb product manager interview guide
• DoorDash product manager interview guide
• Nvidia product manager interview guide

5.2 Learn by yourself

Learning by yourself is an essential first step. We recommend you make full use of the free prep resources on this blog and also watch some mock interviews on our product management YouTube channel. That way you can see what an excellent answer looks like.

Once you’re in command of the subject matter, you’ll want to practice answering questions. But by yourself, you can’t simulate thinking on your feet or the pressure of performing in front of a stranger. Plus, there are no unexpected follow-up questions and no feedback.

That’s why many candidates try to practice with friends or peers

5.3 Practice with peers

If you have friends or peers who can do mock interviews with you, that's an option worth trying. It’s free, but be warned, you may come up against the following problems:

• It’s hard to know if the feedback you get is accurate
• They’re unlikely to have insider knowledge of interviews at your target company
• On peer platforms, people often waste your time by not showing up

For those reasons, many candidates skip peer mock interviews and go straight to mock interviews with an expert.

5.4 Practice with ex-interviewers

In our experience,  practicing real interviews with experts who can give you company-specific feedback makes a huge difference.

Find a product manager interview coach so you can::

• Test yourself under real interview conditions
• Get accurate feedback from a real expert
• Build your confidence
• Get company-specific insights
• Learn how to tell the right stories, better.
• Save time by focusing your preparation

Landing a job at a big tech company often results in a $50,000 per year or more increase in total compensation. In our experience, three or four coaching sessions worth ~$500 make a significant difference in your ability to land the job. That’s an ROI of 100x!