Market sizing course for case interviews

Estimate anything. Out loud. In five steps.

“How much chewing gum do Americans buy in a year?” Questions like this decide first rounds at consulting, strategy and tech firms. This course teaches you one method that works for every one of them, then drills it on 33 fully solved cases.

Watch 5 free lessons See all 38 lessons
38video lessons
33solved cases
5question types
Try it: lesson 6 Perishables

What is the market size of chewing gum in the USA?

$4.4Bper year, retail value
330M × 60% × 11/wk × 50 wks × $0.04
Young children and many older people do not chew gum.
Average of frequent (20), regular (10) and occasional (5) chewers.
A 15-piece pack costs about $0.60.

Sanity check: about $13 per person per year, roughly one pack a month.

Estimation questions come up far beyond consulting.

Management consultingCorporate strategyInvestment bankingProduct and techStart-ups and VC
The method

One process for every estimation question

Interviewers do not score the final number. They score how you got there. These five steps make your thinking easy to follow, every time, in the same order.

1

Understand the problem

Clarify scope before you start, so you never solve the wrong question.

“Are we sizing retail value or manufacturer revenue?”
2

Agree the approach

Say your plan in one or two sentences and check that it sounds right.

“I will start from the number of people who chew gum…”
3

Structure the tree

Draw the logic from left to right, starting from the output, before any numbers.

Market = pieces × price
4

Assume and calculate

Put a number on each leaf, explain why, then round your way to the answer.

330 × 0.6 ≈ 200M
5

Sanity check

Test the answer against something you know before you present it.

$4.4B ÷ 330M ≈ $13 a head
Lesson slide: the chewing gum estimation tree with every number filled in, adding up to $4.4B ▶Chewing gum in the USA · free lesson
Inside a lesson

Watch the tree grow, one step at a time

  1. 01
    Pause and try it firstEvery case stops after the question so you can sketch your own answer.
  2. 02
    Step-by-step walkthroughThe tree builds on screen as the voice-over explains each branch and number.
  3. 03
    Phrases you can reuseLearn exactly what to say to the interviewer at each step.
  4. 04
    Slides to keepDownload every case to revise before your interviews.
Five question types

Spot the type and you already know the structure

About 90% of estimation questions fit one of five types. Each one has a standard tree you can draw in the first minute.

6 cases

Perishables

Things people use up and buy again.

Lipstick in the USA · Takeaway coffee in Moscow

6 cases

Non-perishables

Durable goods people replace every few years.

Smartphones in Brazil · Refrigerators in Italy

7 cases

Units of supply

How many shops, vehicles or people serve a market.

Barbers in London · Yellow cabs in New York

7 cases

Physical estimations

How many things fit in a space, or happen in a place.

Golf balls in a Boeing 737 · Trees saved by the Kindle

7 cases

Financial estimations

Revenue, cost and profit of a single business.

Revenue of a Starbucks store · Airbnb's annual revenue

Not sure which type a question is?

Lesson 3 teaches you how to tell from the key words in the question, and how to handle hybrid cases.

See the curriculum
Curriculum

Short theory, then a lot of practice

Five theory lessons give you the method and the toolkit. Then 33 cases, each solved step by step on screen with a pause to try it yourself first.

AG
Askar Gabzhalilov
Associate Director, InterpathACA · CFA
Your instructor

Learn from someone who does this for a living

I am Askar Gabzhalilov, an Associate Director at Interpath in London. For ten years I have worked at KPMG, FTI Consulting, Efficio and now Interpath, on M&A deals, turnarounds and transformation programmes for FMCG, healthcare, technology and private equity clients.

On almost every one of those projects, the first useful answer was a quick, structured estimate. Before any model is built, someone has to say how big the market is, how much a fix is worth, or whether an idea is worth testing at all.

I have also taught for as long as I have worked. I have mentored students at SEO London since 2016, tutored economics and finance for more than 250 hours, and prepared candidates who went on to join MBB firms. This course is the method I use with them: one clear process, lots of solved cases, and the habit of thinking out loud.

10 yrsconsulting and advisory in London
250+ hrsof one-to-one tutoring
8 yrsmentoring students at SEO London
ACA · CFAChartered Accountant and CFA charterholder
Interpath · Associate DirectorLondon · now
Efficio · Manager2021 to 2025 · Led turnaround and transformation work with C-suite clients, including a €450m working capital programme and the NHS Covid vaccination strategy for 9 million people in England
FTI Consulting · Financial Consultant2019 to 2021 · Valuations and due diligence on £100m+ M&A deals and international arbitration cases
KPMG · Senior Associate2016 to 2019 · Graduate scheme, qualified as a Chartered Accountant
EducationBSc Accounting and Finance, Warwick Business School · MSc Data Science, HSE University
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Pricing

Start free. Upgrade when it clicks.

Watch the first five lessons for free. If the method works for you, unlock everything with one payment and lifetime access. Launch offer: every paid plan is 50% off.

Free

£0
  • Introduction and the 5-step method
  • 3 solved cases: chewing gum, Boeing golf balls, Starbucks
  • Downloadable slides
Start the free lessons
Most popular

Full course

£9950% off
£49 one-off
  • All 38 lessons, theory and cases
  • All 33 cases across the 5 types
  • Anchor numbers and mental maths toolkit
  • Lifetime access and updates
Get the full course

Course + coaching

£39950% off
£199 one-off
  • Everything in the full course
  • Two 1:1 mock interviews with Askar
  • Written feedback after each session
  • Extra sessions £75 each
Book coaching
1:1 coaching

Practise with a real interviewer

Book a live session to run market sizing and case questions under interview conditions, and get direct feedback on your structure, maths and delivery. I have prepared candidates who went on to join MBB firms, and I have run CV clinics for Warwick students.

  • Mock interviews with a market sizing question and a full case
  • Targeted drills on the steps where you lose points
  • CV and fit questions for consulting applications

Write to request a session

Tell me your target firms, your interview dates and what you want to work on.

[email protected]
Message on LinkedIn ↗
Questions

Frequently asked

Do I need a business or maths background?

No. The course uses school-level maths and teaches the rounding tricks you need to calculate quickly and out loud.

Is this only for consulting?

No. Strategy, banking, product and tech roles ask the same questions, and the method works the same way.

How long does the course take?

The theory takes about an evening. Most students then work through two or three cases a day for one to two weeks before interviews.

Will I get the right number?

There is rarely one right number. You will learn to reach a sensible answer with clear logic, which is what interviewers score.