Consulting and Sector Knowledge Guesstimates for PM Sizing Drills
After HR, Ops & Analytics Domain Guesstimates + Drills, the next jump is from function-led sizing to domain-led sizing. In consulting and sector knowledge guesstimates, the answer depends less on a generic population funnel and more on whether you choose the right industry anchor, penetration assumption, productivity metric, and sanity check. This matters in interviews at firms like McKinsey and BCG because the interviewer is testing business judgement, not just arithmetic.
- Consulting guesstimates typically start with consultant headcount, revenue per consultant, project mix, or market-wide advisory spend.
- Sector knowledge guesstimates typically start with an industry anchor such as total 2-wheeler units, airport passengers, data-centre MW capacity, or diagnostic test volumes.
- The MBB India revenue example uses ~6,500 consultants across McKinsey, BCG, and Bain, ~₹2.5 crore annual revenue per consultant, and a ~55% India-client project share.
- The electric 2-wheeler example projects FY28 sales from a FY26 total 2W base of ~1.9 cr units, ~5% annual 2W growth, and ~18% EV penetration.
- A strong answer separates the anchor, penetration, productivity metric, mix adjustment, and sanity check before doing the final math.
- The best sanity checks use a second source of logic, such as per-consultant revenue for MBB or a bottom-up stack of Ola, TVS, Bajaj, Ather, and tail brands for EV-2W.
From Functional Guesstimates to Domain-Led Sizing
In functional guesstimates, the tree often begins with people, households, transactions, or utilisation. In consulting and sector knowledge drills, the starting point is usually an industry structure: how firms make money, how capacity converts into revenue, how penetration evolves, and how named players add up.
The big picture is simple: pick the industry anchor first, then build the sizing tree around the metric that actually drives the sector.
A domain-led guesstimate sizes a market or activity by starting with the sector's natural business driver: for consulting, this may be consultant headcount or fee pool; for sectors, it may be units sold, capacity, passengers, tests, or registrations.
For McKinsey, BCG, and Bain combined in India, the source sizes ~6,500 consultants: McKinsey ~3,000, BCG ~2,500, and Bain ~1,000. At ~₹2.5 crore annual revenue per consultant, total revenue is ~₹16,250 crore, with a ~55% India-client portion of ~₹8,940 crore and offshore-servicing portion of ~₹7,300 crore. The strategic so what: in a consulting sizing answer, headcount and productivity often explain revenue better than a population funnel.
Why Consulting Guesstimates Need a Firm Economics Lens
Consulting questions often ask for revenue, fee pools, number of pitches, mandates, or professionals. That means the natural unit is not a consumer or household; it is usually a consultant, partner, project, client mandate, or percentage fee.
MBB refers to McKinsey, BCG, and Bain, the three strategy consulting firms named in the source. A consulting guesstimate for these firms should usually separate local India work from offshore or capability-centre work, because the MBB example explicitly splits India-client revenue and offshore-servicing revenue.
The important nuance is ownership of the revenue pool. For example, total MBB India revenue includes both India-client projects and offshore servicing for global work. In many interview answers, candidates lose accuracy by mixing these two without calling out the split.
Worked Example - Annual Revenue of MBB Consulting Firms in India
This answer works because it mirrors consulting economics: people deliver projects, utilisation converts time into revenue, and the mix of local versus offshore work changes the interpretation of the final number. The interviewer can challenge any assumption, but the structure remains defensible.
Why Sector Knowledge Guesstimates Need an Industry Anchor
Sector questions test whether you understand what drives demand or revenue in that industry. Electric 2-wheelers, data centres, airports, diagnostic labs, MSME registrations, and health insurance claims all require different anchors.
EV means electric vehicle, and 2W means two-wheeler. In the electric-scooter example, the right anchor is not India's population; it is total 2W market size, expected 2W growth, and EV penetration.
The nuance is that a sector anchor must match the unit of the answer. If the interviewer asks for electric-scooter revenue, move from units to price using the source average of ₹1.1 L per unit. If the interviewer asks for passenger movement, do not force a revenue metric; divide annual passenger traffic by days.
Worked Example - FY28 Electric-Scooter Sales in India
This is a strong product-manager style sizing answer because it connects market growth, penetration, pricing, and competitive reality. The named-player sanity check is especially useful: Ola, TVS, Bajaj, and Ather provide a bottom-up lens that makes the top-down projection feel commercially real.
Reusable Decision Framework for Consulting and Sector Drills
Use this framework whenever the prompt sounds domain-heavy: consulting firm revenue, advisory fee pools, EV sales, data centres, diagnostic labs, insurance claims, or airport volumes. The goal is to make the first anchor choice explicit before you calculate.
In many interviews, the framework matters as much as the final number. A candidate who says "I will anchor on total 2W units rather than population because the question is about vehicle sales" shows better judgement than a candidate who rushes into arithmetic.
Structuring a Consulting & Sector Knowledge Domain Guesstimates + Drills Interview Answer
"Estimate annual electric-scooter sales in India for FY28 and the revenue opportunity."
The number one way candidates get this wrong is by starting from India's population instead of the sector's actual demand driver. For EV-2W, the right anchor is total 2W units and EV penetration; for MBB revenue, the right anchor is consultant headcount and revenue per consultant.
Conclusion
Consulting and sector guesstimates are domain-led sizing drills: choose the right anchor, apply the right penetration or productivity metric, calculate a clear range, and sanity-check with a second business lens. If your first anchor matches the sector's economics, the rest of the answer becomes easier to defend.
The most frequent error is using a generic population funnel for every problem. That costs points because McKinsey, BCG, and similar interviewers expect the anchor to change by domain: consultants for MBB revenue, total 2W units for electric scooters, MW capacity for data centres, and test volumes for diagnostic labs.