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For market sizing, how do I choose between a demand-side and supply-side approach?

Market Sizing

For some market-sizing questions I can see both a customer-demand approach and a supply/capacity approach. How do I decide which one to use in the interview?

9 hours agoCanada

Top answer Mayank G.

Mayank G.Coach

Choose the approach that uses the most reliable assumptions and connects most directly to the market you are sizing.

Interviewer gave me a starting population number that seems wrong. Should I challenge it?

Market Sizing

In a market-sizing case, the interviewer gave me a population figure that did not match what I thought was correct. I froze because I did not know whether it was a test or just a simplified assumption. Should you challenge a number the interviewer gives you if you think it is wrong?

Sep 29, 2026United States

Top answer Mayank G.

Mayank G.Coach

Use the number provided for the case unless there is a clear reason to clarify what it represents.

Should I state all my market-sizing assumptions upfront, or introduce them only when I need them?

Market Sizing

When I do market sizing, I sometimes spend a long time listing every assumption before calculating anything. Other people seem to introduce assumptions step by step. Which approach is clearer in an interview?

Oct 7, 2026Hong Kong SAR China

Top answer Mayank G.

Mayank G.Coach

State the key structural assumptions upfront, then introduce lower-level assumptions when they become relevant.

In market sizing, should I replace a rough assumption with a real number I happen to know?

Market Sizing

Sometimes a market sizing case asks me to estimate something like population or household size, but I actually know the real number. Should I use it, or is the interviewer expecting me to make an assumption and show the logic?

Oct 6, 2026United States

Top answer Mayank G.

Mayank G.Coach

If you genuinely know a reasonable real-world number, you can use it. The goal is not to pretend you know less than you do.

Should I use households or individuals as the base in a market sizing case?

Market Sizing

I sometimes get stuck at the first step because I cannot tell whether to size from total population, households, or some other unit. Is there a general rule for choosing the base, or does it depend entirely on what is being bought?

Sep 30, 2026United States

Top answer Mayank G.

Mayank G.Coach

Use the unit that best matches how the product is purchased or consumed.

What is the best way to practice market sizing and actually get better at it?

Market Sizing

I want market sizing practice drills to get better at it. What is the best way to practice market sizing?

Oct 1, 2026United States

Top answer Mayank G.

Mayank G.Coach

Practice the underlying steps repeatedly: define the market, choose a sensible approach, make transparent assumptions, calculate accurately, and sanity-check the result.

What do you do when a market-sizing answer changes a lot based on one assumption?

Market Sizing

In one practice market sizing case, changing a single penetration assumption moved the answer by almost 2x. I was not sure whether that meant my structure was bad or whether I was supposed to call out how sensitive the estimate was. How should you handle that during an interview?

Sep 24, 2026Germany

Top answer Mayank G.

Mayank G.Coach

Call out the sensitivity. A market-sizing estimate can still be useful even when one assumption has a large effect, as long as you recognize which assumption is driving the range.

BCG gave me a market sizing and I completely panicked on the assumptions

Market Sizing

I had a market sizing in an interview and the structure itself was okay, but once I got into assumptions I felt lost. I kept second-guessing whether the numbers were reasonable, which made the whole thing much slower than it should have been. How do people get better at making assumptions confidently without sounding like they are just making things up?

Jul 18, 2026Canada

Top answer Mayank G.

Mayank G.Coach

The key is to remember that assumptions are not judged on exact precision. They are judged on whether they are reasonable, transparent, and internally consistent.

What do you do when you don't know a market-sizing input?

Market Sizing

In market sizing I sometimes get stuck because I genuinely do not know an input, like average store traffic or household spending on a niche product. Are you supposed to ask the interviewer, make an assumption, or find a different way to structure the estimate?

Jun 28, 2026United Kingdom

Top answer Mayank G.

Mayank G.Coach

Do not freeze just because you do not know a real-world fact. State that you do not know the exact figure, propose a reasonable assumption, and explain the logic behind it.

Bottom-up vs top-down market sizing: which should you use?

Market Sizing

I understand the definitions, but in a real case how do you decide whether to size a market top-down or bottom-up? Is one approach viewed as stronger in interviews, or is it just whichever gets you to a reasonable answer faster?

Jun 19, 2026Singapore

Top answer Mayank G.

Mayank G.Coach

Neither method is automatically better. The stronger approach is the one that fits the information available and lets you explain the market logically.

How do you make assumptions in market sizing without sounding random?

Market Sizing

My biggest issue with market sizing is not the framework. It is the assumptions. I always worry the numbers I choose sound arbitrary, so I end up hesitating too much. What is the best way to make assumptions feel more grounded?

Apr 18, 2026Germany

Top answer Mayank G.

Mayank G.Coach

Try to base assumptions on simple reference points instead of isolated guesses. Population ranges, household size, usage frequency, and comparable categories are all examples of anchors that can make your logic feel much more credible.

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Community Forum

For market sizing, how do I choose between a demand-side and supply-side approach?

Interviewer gave me a starting population number that seems wrong. Should I challenge it?

Should I state all my market-sizing assumptions upfront, or introduce them only when I need them?

In market sizing, should I replace a rough assumption with a real number I happen to know?

Should I use households or individuals as the base in a market sizing case?

What is the best way to practice market sizing and actually get better at it?

What do you do when a market-sizing answer changes a lot based on one assumption?

BCG gave me a market sizing and I completely panicked on the assumptions

What do you do when you don't know a market-sizing input?

Bottom-up vs top-down market sizing: which should you use?

How do you make assumptions in market sizing without sounding random?