Market Sizing: Case Interview Framework

Key Insights:

• Annual Revenue Is The Default: Most market sizing questions ask for the yearly dollar value of a market. If the interviewer doesn't say otherwise, solve for that.
• Use One 5-Step Framework: Clarify scope, share your approach, state assumptions, run the math out loud, and end with an insight. The whole answer should take 8 to 10 minutes.
• Logic Beats Precision: Within 10x of the real number is a good answer, and within 25% is a great one. Interviewers score how you think more than where you land.

Market sizing is one of the most common exercises in a case interview. You'll see it as a standalone question in early rounds and as the math step inside longer cases at McKinsey, Bain, BCG, the Big 4 and boutique firms. This guide gives you the 5-step market sizing framework interviewers expect, top-down and bottom-up worked examples, a 2026 cheat sheet of numbers to memorize, and 25 practice questions with answers. The exercise mirrors real consulting work. You build a small model on paper with estimated inputs, then walk your interviewer through it the way you'd walk a client through a spreadsheet. If you can do that calmly in an interview, you can do it in front of a client CEO.

What Is Market Sizing?

Market sizing is the process of estimating the total market for a product or service. In consulting, it most often means the annual revenue of a market: how many dollars customers spend on something in one year. Strategy work starts here, because a client needs to know how big the prize is before deciding whether to chase it. In a case interview, you might be asked to size the market for diamond rings in Denmark or disposable diapers in Texas. There's rarely a single right answer. The interviewer wants a structured, logical path to a reasonable number.

What Are The Five Types Of Market Sizing Answers?

Every market sizing question asks for one of five answers. Confirm which one at the start, because it decides which steps you need.

1. Total Units: The number of items in use today, no matter when they were bought. Example: "How many cars are there in California?"
2. Total Value: The value of all items in use today. Interviewers rarely ask for this one.
3. Annual Units: The number of items sold in one year. Example: "How many cars were sold in Mexico last year?"
4. Annual Value: The dollars spent on the item in one year. This is the default, and more than 90% of market sizing questions ask for it.
5. Client Share: The client's sales as a percentage of the annual market. Example: "What is the opportunity if our client launches a hybrid car in Mexico?"

If you're unsure, say, "I'll assume you're looking for annual revenue. Is that right?" That one sentence shows the interviewer you scope before you calculate.

How Does Market Sizing Relate To TAM, SAM And SOM?

Founders and investors describe market size in three layers. TAM (total addressable market) is all spending on the product. SAM (serviceable addressable market) is the part your business model and geography can reach. SOM (serviceable obtainable market) is the share you can realistically win. A case interview usually asks for the TAM, measured as annual value. A "client share" or "opportunity" question moves you down to the SOM. You don't need the acronyms in the interview, but knowing them helps you read the question correctly.

Why Do Consulting Firms Ask Market Sizing Questions?

Firms use market sizing to test three skills at once: structure, problem-solving and communication. It's a fast way to see how you'll handle an ambiguous client question with no data.

• Structure: Can you lay out a logical, step-by-step approach before touching a number?
• Problem-Solving: Can you make sensible assumptions, run quick and accurate calculations, and reach an answer that makes sense in the time allowed?
• Communication: Can you explain your logic so clearly that the interviewer follows without looking at your paper?

How Do Interviewers Score A Market Sizing Answer?

Interviewers grade the process first and the number second. Strong market sizing answers share four traits:

• A clear plan before the math begins.
• Realistic assumptions you can defend.
• Clean arithmetic, spoken out loud.
• A short, confident summary that sounds client-ready.

On the number itself, use this benchmark. A good answer lands within one order of magnitude (10x) of the real figure, and a great answer lands within 25%, if a real figure exists.

What Is The 5-Step Market Sizing Framework?

The market sizing framework has five steps: clarify scope, share your approach, state your assumptions, calculate out loud, and end with an insight. Plan on 8 to 10 minutes from the question to your final answer. Here is how the time breaks down.

Step	Time
1. Clarify Scope	About 1 minute
2. Share Your Approach	About 2 minutes
3. State Your Assumptions	About 2 minutes
4. Calculate Out Loud	2 to 3 minutes
5. End With An Insight	1 to 2 minutes
Total	8 to 10 minutes

Step 1: Ask Clarifying Questions To Limit Scope

Before any numbers, confirm exactly what you're sizing. Consultants never start an analysis without scoping it, and neither should you.

• Answer Type And Units: "When you ask me to size the market for diamond rings in Denmark, I assume you want annual revenue. Can you confirm?"
• Geography: "When you say North America, can I focus on the U.S. and Canada?"
• Customer Type: "The residential dishwasher market is likely much larger than the commercial one. Can I focus there?"
• Product Definition: "For bicycles, I'll include manual, two-wheel bikes only. Is that okay?"
• Exclusions: Name what's out of scope, such as accessories, repairs or the secondhand market.

Step 2: Walk The Interviewer Through Your Approach

Tell the interviewer what you'll do before you do it. Lay out a simple list of 5 to 7 steps, with no numbers yet. For a top-down approach, the list usually looks like this: population or households, one segmentation, the share who buy or use the product, how often they buy, and the average price. Pick one way to segment the market, such as age, income or household type. One level of segmentation is enough. End with a question: "How does this approach sound to you?" That shows you can lead with a point of view while staying open to feedback, which is the balance top firms want.

Step 3: Walk The Interviewer Through Your Assumptions

Now go back through your steps and plug in a number for each one. Explain where each number comes from, whether that's personal experience, background knowledge or a known fact.

• Use round numbers that are easy to multiply, such as a U.S. population of about 340 million.
• Give a one-line reason: "Most adults own one phone and replace it every two or three years."
• Use facts you know: "The average U.S. household has about 2.5 people."

Close with "How do these assumptions sound?" Expect pushback. Hold your ground when your logic is sound, and adjust when the interviewer gives you a better number. More pushback usually means the interviewer is engaged, not that you're failing.

Step 4: Walk The Interviewer Through Your Calculations

Do the math out loud so the interviewer can follow and you can catch slips early. Write partial results clearly so you can refer back to them.

• Multiply in short steps and keep track of your units and zeros.
• Round to easy numbers as you go, and keep the rounding consistent.
• If you make a mistake, correct it calmly and move on. Catching your own error is a good sign.

Practice this step with our free math drills and the methods in our case interview math guide.

Step 5: End With An Insight

Finish the way you'd brief a client: headline first, then drivers, then insight. Run a quick sanity check before you speak.

1. Headline: "The U.S. market is about $15 billion a year."
2. Drivers: Name the one or two segments that drive most of that number.
3. Insight: Say what it means. Is the market large or small for this client? What would you explore next?

Top-Down Vs Bottom-Up Market Sizing: Which Should You Use?

Top-down market sizing starts with a large population and narrows it to buyers. Bottom-up market sizing starts with one store, machine or location and scales up. Top-down is our default in case interviews because population data is easy to recall, but either method can solve any question.

	Top-Down	Bottom-Up
Starting Point	Population or households	One unit of supply: a store, machine, route or location
Typical Steps	Population, segment, % who buy, purchases per year, price	Number of locations, sales per location per day, days per year, price
Best For	Consumer products most people buy	Businesses with physical locations or capacity limits
Watch Out For	Unrealistic usage rates across a huge base	Forgetting slow hours, weekends and holidays

The two methods often give different answers, and that's fine. They should land in the same range, not orders of magnitude apart. If they don't, one of your assumptions is off.

Top-Down Example: How Big Is The U.S. Bottled Red Wine Market?

This is a consumer product with wide use but different habits by age, so top-down works well. Start with about 340 million people in the U.S., or roughly 250 million adults of drinking age, and split them into three age groups.

Age Group	People	% Who Drink Red Wine	Bottles Per Year	Price Per Bottle	Annual Spend
21 to 40	87.5M	30% (26.25M)	12	$12	$3.8B
41 to 60	87.5M	40% (35M)	18	$18	$11.3B
61+	75M	25% (18.75M)	10	$15	$2.8B
Total	250M	80M drinkers			About $18B

Answer: The U.S. bottled red wine market is about $18 billion a year. The 41 to 60 group drives more than 60% of it, because they drink more often and pay more per bottle. That's where a wine brand would focus first.

Bottom-Up Example: How Big Is The U.S. Coffee Shop Market?

Coffee shops have a hard cap on how many customers they can serve, so bottom-up works well. Size one shop, then multiply.

1. Customers Per Day: 3 peak hours at 60 customers an hour is 180. Another 10 slower hours at 20 an hour is 200. That's about 380 customers a day.
2. Average Ticket: About $7 per order, or roughly $2,660 a day.
3. Days Per Year: Open about 360 days, so roughly $960,000 a year. Round to $1 million per shop.
4. Number Of Shops: Assume about 40,000 coffee shops in the U.S.

Answer: 40,000 shops times $1 million is about $40 billion a year. Sanity check: the largest U.S. chain alone reports more than $20 billion in U.S. sales, so a total near $40 billion passes the gut check.

Client Share Example: What Is The Opportunity For A Hybrid Car In Mexico?

An "opportunity" question starts with the annual market, then asks how much your client can win. Size the annual market first, then apply a share.

1. Cars In Use: About 130 million people live in about 35 million households. If half the households own a car, that's about 17.5 million cars.
2. Annual Units: Cars are replaced about every 10 years, so about 1.75 million new cars are sold a year.
3. Hybrid Share: Assume 5% of new cars are hybrids, or about 90,000 a year.
4. Client Share: Assume the client wins 20% of hybrid sales, or about 18,000 cars.
5. Value: At about $30,000 per car, that's roughly $540 million a year.

Answer: The opportunity is about $500 million a year in revenue. A strong close adds the so-what: "That's meaningful, but it depends on the client winning one in five hybrid buyers. I'd want to test that share against current competitors next."

Worked Example: How Big Is The Market For Bicycles In Italy?

Here is the full 5-step market sizing framework applied to one question: "Size the market for bicycles in Italy." The answer is about €1.9 billion a year. Step 1, Clarify: We confirmed the interviewer wants annual revenue, and we focused on residential bicycles only. E-bikes, rentals and used bikes are out of scope. Step 2, Approach: Population of Italy, split into four age groups, the share of each group who owns a bike, how often they replace it, and the average price. Step 3, Assumptions: Italy has about 60 million people, spread evenly across four age groups of 15 million each.

Age Group	People	% Who Own	Replace Every	Bikes Bought Per Year	Avg Price	Annual Spend
0 to 20	15M	70% (10.5M)	2 years	5.25M	€100	€525M
21 to 40	15M	60% (9M)	4 years	2.25M	€400	€900M
41 to 60	15M	50% (7.5M)	6 years	1.25M	€300	€375M
61+	15M	30% (4.5M)	10 years	0.45M	€300	€135M
Total	60M	31.5M owners		9.2M		€1.935B

Step 4, Calculate: For each group, owners divided by years between purchases gives bikes bought per year. Multiply by price and add the four groups. The result is about 9.2 million bikes and €1.9 billion a year. Step 5, Insight: "The Italian bicycle market is about €1.9 billion a year, and adults 21 to 40 drive almost half of it because they buy the most expensive bikes." Then sanity-check the units. New bicycle sales in Italy run in the low millions a year, so 9.2 million is likely several times too high. It's still within 10x, which makes it a good answer. To make it great, name the lever that's off: children's bikes get handed down, so replacing every two years overstates new purchases. That last move is what separates strong candidates. You don't need to know the real number, but you should spot which assumption would move your answer the most.

What Numbers Should Be On Your Market Sizing Cheat Sheet?

A market sizing cheat sheet is a short list of anchor numbers you memorize so you can start any question fast and sanity-check your answer. These are rounded for interview math, which is exactly how you should use them.

U.S. Population	About 340 million
U.S. Households	About 130 million (about 2.5 people each)
U.S. Adults (18+)	About 265 million
People Per Year Of Age (U.S.)	About 4 million (assume an even spread from 0 to 80)
U.S. Births Per Year	About 3.6 million
U.S. Workforce	About 170 million
U.S. Median Household Income	About $80,000
U.S. GDP	About $30 trillion
U.S. K-12 Students	About 50 million
U.S. College Students	About 19 million
U.S. Registered Vehicles	About 285 million
U.S. New Car Sales Per Year	About 16 million
U.S. Small Businesses	About 35 million (about 6 million have employees)
World Population	About 8.2 billion
China / India	About 1.4 billion each
European Union	About 450 million
UK / Germany / Italy	About 70 million / 84 million / 60 million
Canada / Mexico / Japan	About 40 million / 130 million / 125 million
Time	365 days, about 250 working days, 8,760 hours a year

Download the Market Sizing Cheat Sheet (PDF) and our Market Sizing Template so you always have the framework and these numbers on hand.

25 Market Sizing Questions With Answers

The best way to build market sizing speed is to work through many questions across industries. Try each one out loud before you read the approach. Your numbers can differ from ours. What counts is a clean structure and an answer in the same range.

Consumer Market Sizing Questions

Question	Approach	Answer
1. How big is the U.S. disposable diaper market?	About 8M children in diapers (roughly 2.25 years of births) x 6 diapers a day x 365 = about 17.5B diapers x $0.30	About $5B a year
2. How many electric toothbrush heads are sold in the U.S. each year?	340M people x 25% use electric brushes = 85M x 4 heads a year	About 340M heads (about $1.7B at $5 each)
3. How big is the U.S. pizza delivery market?	130M households x 50% order delivery x 12 orders a year x $25	About $20B a year
4. How many golf balls are sold in the U.S. each year?	25M golfers x 15 rounds a year x 2 balls lost per round	About 750M balls (about $1.1B at $1.50 each)
5. How big is the U.S. movie ticket market?	340M people x 60% go to movies x 3 visits a year = about 600M tickets x $11	About $6.6B a year
6. How big is the U.S. dog food market?	130M households x 40% own a dog x 1.5 dogs = about 80M dogs x $40 a month x 12	About $38B a year

B2B And Industrial Market Sizing Questions

Question	Approach	Answer
7. How big is the U.S. office printer paper market?	170M workers x 40% in offices = 68M x 10 sheets a day x 250 days = 170B sheets / 500 per ream = 340M reams x $8	About $2.7B a year
8. How big is the U.S. car wash market?	285M vehicles x 50% use car washes x 10 washes a year x $12	About $17B a year
9. What is the annual revenue of one large airport parking garage?	Bottom-up: 5,000 spaces x 80% full x $25 a day x 365 days	About $36M a year
10. How big is the U.S. restaurant point-of-sale terminal market?	1M restaurants x 3 terminals, replaced every 5 years = 600K terminals a year x $1,500	About $900M a year
11. How big is the U.S. heavy truck tire replacement market?	4M heavy trucks x 18 tires, replaced every 3 years = 24M tires a year x $400	About $9.6B a year

Healthcare Market Sizing Questions

Question	Approach	Answer
12. How many MRI scans are done in the U.S. each year?	340M people x about 12% get one scan a year	About 40M scans
13. How big is the U.S. contact lens market?	265M adults x 15% wear contacts = about 40M x $150 a year	About $6B a year
14. How big is the U.S. flu shot market?	340M people x 45% vaccinated = about 150M doses x $40	About $6B a year
15. How big is the U.S. hearing aid market?	265M adults x 15% with hearing loss = 40M x 30% use aids = 12M, replaced every 5 years = 2.4M buyers x 2 aids x $2,000	About $9.6B a year

Technology And Media Market Sizing Questions

Question	Approach	Answer
16. How many smartphones are sold in the U.S. each year?	About 260M users (adults and teens), replaced every 2.5 years	About 105M phones (about $63B at $600 each)
17. How many laptops do U.S. college students buy each year?	19M students x 90% buy one, replaced every 4 years	About 4.3M laptops (about $3.9B at $900 each)
18. How big is the U.S. video streaming subscription market?	130M households x 85% subscribe x 3 services x $15 a month x 12	About $60B a year
19. How big is the U.S. home EV charger market?	About 1.3M new EVs a year x 60% install a home charger x $1,200 installed	About $1B a year
20. How big is the U.S. video game console market?	130M households x 45% own a console, replaced every 6 years = about 10M consoles x $450	About $4.5B a year

Public Sector And Transportation Market Sizing Questions

Question	Approach	Answer
21. How many school buses are there in the U.S.?	50M K-12 students x 50% ride a bus = 25M / 50 students per bus	About 500K buses
22. How many gas stations are there in the U.S.?	285M vehicles x 1 fill-up a week / 7 = about 41M fill-ups a day / 350 fill-ups per station	About 120K stations
23. How many U.S. passports are issued each year?	340M people x 50% hold a passport, renewed every 10 years = 17M, plus about 5M first-time applicants	About 22M passports
24. How many streetlights are there in the U.S.?	4.2M miles of road x 25% lit x 35 lights per mile (one every 150 feet)	About 37M streetlights
25. How many passengers pass through the busiest U.S. airport each year?	2,500 flights a day x 150 seats x 80% full = 300K passengers a day x 365	About 110M passengers

Want unlimited fresh questions? Our market sizing drills generate a new product and region every time, with a step-by-step answer template. You can also practice full cases with market sizing in the MC Case Library.

How Should You Communicate Your Market Sizing Answer?

Communicate your market sizing answer the way a consultant presents to a client: approach first, assumptions with reasons, clean math, then the headline and what it means. Perfect math won't save a confusing delivery.

1. State Your Approach: "I'll start with U.S. households and segment by income."
2. Explain Each Assumption: "I'll assume 5% of households own an electric vehicle, based on how many I see in a typical neighborhood."
3. Show Your Math: Speak slowly and check each step as you go.
4. Give The Headline And So-What: "Based on these assumptions, the market is about $15 billion a year, which is large enough to justify a dedicated product line."

What Are The Most Common Market Sizing Mistakes?

The most common market sizing mistakes are jumping into math too fast, making extreme assumptions, losing track of zeros, and skipping the sanity check. Each one is fixable with practice out loud.

• Jumping Into Math: Always clarify scope and share your approach first.
• Extreme Assumptions: If you assume 0% or 100% of a group does anything, your credibility drops.
• Messy Math: Inconsistent rounding and skipped steps make you hard to follow.
• Too Much Segmentation: One clean cut, such as age or income, beats three layers you can't finish in time.
• No Sanity Check: Reporting a number without asking, "Does this make sense?"
• No Insight: Ending on a number instead of what it means for the client.

How Do You Sanity-Check A Market Size?

Compare your answer to a number you already know, and ask whether it's in the same range. If you sized U.S. coffee shops at $400 billion, compare it to a U.S. GDP of about $30 trillion: that would put coffee at more than 1% of the whole economy, which is too high.

• Per-Person Check: Divide your total by the population. Does that spend per person feel right?
• Known-Market Check: Compare to a market you know, such as about 16 million new cars sold in the U.S. each year.
• Two-Method Check: Run a quick bottom-up version of a top-down answer. The two should land in the same range.

Remember the benchmark: within 10x is good, within 25% is great. If your check shows you're far off, say so and name the assumption you'd change. Interviewers reward that self-correction.

Market Sizing Video Walkthrough

Watch an MC coach walk through a market sizing case from the first clarifying question to the final answer.

How Do You Practice Market Sizing?

Practice market sizing with short, repeated drills, out loud, across many industries. Speed and confidence come from volume, not from reading more examples. Our market sizing drills give you a random product and region every time, so you can't memorize the answer. Work through about five drills in a row: focus first on structure, then on adding a segmentation, then on calculation speed. When you spot a weak step, drill that step alone. Unlimited drills come with the All Access Pass, along with MC's full case curriculum. When you're ready for expert feedback, our Black Belt program pairs you 1:1 with a former McKinsey, Bain or BCG consultant. 80% of Black Belts earn at least one offer, compared with an industry average of about 3%. Market sizing feels uncomfortable at first because there's no data and no single right answer. That's exactly why it's so learnable: every question follows the same five steps. Start your first drill today, and within a few weeks you'll size markets as naturally as a working consultant.

Additional Resources:

• Case Interview: The Complete Prep Guide
• Case Interview Frameworks: Ultimate Guide
• Case Interview Math
• Top Consulting Firms of 2026
• Top 10 U.S. Boutique Consulting Firms (2026)
• Consulting Firm Directory
• MC Job Board
• Consulting Resume: Complete Guide

Market Sizing FAQs