Framework Market Sizing

The Two Core Approaches

Market sizing questions are a staple of consulting interviews. They test your logical thinking, quantitative skills, and ability to make reasonable assumptions. The goal isn't to find the exact right answer, but to demonstrate a structured approach. There are two primary methods: Top-Down and Bottom-Up.

Top-Down Approach

Start with a large, known population and narrow it down through logical segmentation and assumptions.

Example: The annual market size for smartphones in Saudi Arabia

Start with the total population of Saudi Arabia (~35 million).
Segment by age to find the relevant population (e.g., 80% are between 15-65 years old).
Estimate smartphone penetration within that group (e.g., 95%).
Estimate the average replacement cycle (e.g., people buy a new phone every 3 years, so 1/3 of users buy a new phone annually).
Calculate: (35M * 80% * 95% * 33%) = ~8.8 million phones sold per year.
Multiply by the average smartphone price (e.g., 2,500 SAR) to get the market value.

Bottom-Up Approach

Start with an individual unit or segment and build up to estimate the total market.

Example: The number of coffee cups sold in Riyadh daily

Segment the population of Riyadh (~8 million) into logical groups (e.g., office workers, students, others).
For each group, estimate the number of people and their daily coffee consumption. Office workers (2M people * 1.5 cups/day), Students (1M people * 1 cup/day), Others (5M people * 0.2 cups/day).
Calculate the total cups for each segment: (2M * 1.5) + (1M * 1) + (5M * 0.2) = 3M + 1M + 1M = 5 million cups.
State your assumptions clearly (e.g., 'I assume office workers drink more coffee on average').

Sanity-Checking Your Results

After you have your final number, it's crucial to take a moment to sanity-check it. This shows the interviewer that you have business acumen and can critically evaluate your own work.

Validation Checklist

Cross-check with another method: If you used a bottom-up approach, can you quickly try a top-down approach to see if the numbers are in the same ballpark?
Per-capita check: Does the final number make sense on a per-person basis? (e.g., "Does 5 million cups a day in an 8-million-person city seem reasonable? Yes, it's about 0.6 cups per person, which sounds plausible.")
Compare to known data points: Can you relate it to something you know? "The global smartphone market is X, so my number for Saudi Arabia being Y% of that seems reasonable."
Review your assumptions: Which assumption has the biggest impact on your result? Acknowledge this and briefly discuss how a change in that assumption would affect the outcome.