In a typical first round of eight, two or three prompts are pure sizing. The interviewer is not grading a memorized TAM. They are grading whether you pick the right structure in the first fifteen seconds, then keep units through a short chain.
This page is the question bank. The full method lives on market sizing step by step; pure "how many" Fermi chains live on guesstimate interview questions. After this, you should open any prompt below, name the structure, write a one-line first cut, and finish five with a public-statistic check.
What the sheet rewards on a sizing question
A sizing question is a short case. The sheet pays for four things, in order:
| What they score | What it looks like | What kills the score |
|---|---|---|
| Object | Geography, product, customer, year, value vs volume | Resizing "the market" when they asked bags |
| Structure | Stock, flow, value, capacity, or B2B funnel named aloud | Pasting a US-household funnel onto every prompt |
| Chain | Three to six factors with units | Six decimals, no units, then a round number |
| Sanity | One ceiling or comparable you can defend | Treating 26,000,000 as a census count |
I stop listening when the first factor is "US population" and the question was about kiln capacity in Kenya. Change the first factor to match the object.
How to use this bank
Do not memorize answers. For each prompt, say the structure type out loud, write the first cut in one line, then run the chain on paper in five minutes. Checklist before you start:
- Value ($ / year) or volume (units / year) or stock (installed base)?
- Consumer, B2B, or capacity-constrained?
- US default or a named geography?
CoachNed's timed sizing drills live at /drills/market-sizing. A randomizer that serves fresh prompts is at /tools/market-sizing-questions.
Twenty-five prompts by structure type
Each row is an original prompt plus a one-line first cut. The five marked worked are fully solved below.
Consumer value ($ / year)
| # | Prompt | First cut |
|---|---|---|
| 1 | Annual US spend on meal-kit subscriptions | Households × share that subscribe × $/box × boxes/year (worked) |
| 2 | Annual US spend on residential HVAC service contracts | Housing units with central HVAC × share under contract × $/year |
| 3 | Annual US spend on pet dental chews | Dog-owning households × share that buy chews × $/year |
| 4 | Annual US spend on bicycle helmets (new sales) | Cyclists × helmets bought per year × $/helmet |
| 5 | Annual UK spend on private gym memberships | UK adults × gym membership rate × £/year (worked) |
Consumer volume (units / year)
| # | Prompt | First cut |
|---|---|---|
| 6 | Athletic shoes sold in the US per year | Population × shoes/person/year (worked) |
| 7 | Bags of bagged ice sold in US grocery per year | Households × summer weeks × bags/week × grocery share |
| 8 | Disposable coffee cups used in US offices per day | Office workers × cups/worker/day |
| 9 | Replacement smartphone screens sold in the US per year | Phone stock × annual crack rate × repair share |
| 10 | Pairs of ski goggles sold in the US per year | Skiers × goggles bought per skier-year |
B2B and enterprise
| # | Prompt | First cut |
|---|---|---|
| 11 | Annual US spend on warehouse forklift maintenance contracts | Forklift installed base × share under contract × $/year |
| 12 | Annual US spend on CRM seats for mid-market software firms | Mid-market firm count × seats/firm × $/seat/year |
| 13 | Annual US spend on commercial roof coating | Commercial roofs × share recoated/year × $/roof |
| 14 | Annual US spend on fleet telematics subscriptions | Commercial vehicles × telematics attach rate × $/vehicle/year |
Installed base (stock, not flow)
| # | Prompt | First cut |
|---|---|---|
| 15 | Active general-aviation aircraft in the US | Pilots × aircraft per active pilot, then check FAA (worked) |
| 16 | Commercial espresso machines installed in US cafes | Cafe count × machines per cafe |
| 17 | MRI machines installed in England | Hospitals × scanners per hospital (stock) |
| 18 | Residential heat pumps installed in the US | Housing units × heat-pump penetration |
Capacity and constrained supply
| # | Prompt | First cut |
|---|---|---|
| 19 | MRI scans a 300-bed US hospital can run per year | Machines × hours/day × days × scans/hour |
| 20 | Passenger boardings a single mid-size US airport gate can handle per day | Turns/day × seats × load factor |
| 21 | Tons of ready-mix concrete one mixer truck can deliver per day | Loads/day × m3/load × density |
Non-US and emerging-market
| # | Prompt | First cut |
|---|---|---|
| 22 | 50 kg bags of retail cement sold in Kenya per year | Households × share doing a cement job × bags/job |
| 23 | Annual spend on prepaid mobile top-ups in Nigeria | Population × prepaid share × top-ups/year × $/top-up |
| 24 | Motorbike helmets sold in Vietnam per year | Motorbike stock × helmets bought per bike-year |
| 25 | Annual India spend on packaged drinking water (PET bottles) | Urban population × bottles/person/year × Rs/bottle (worked) |
Ned's rule. Name the structure before you name a number. If you cannot say stock, flow, value, capacity, or B2B in one breath, you do not yet have a question — you have a panic reflex.
Five worked answers (reproduce the arithmetic)
Each answer anchors one factor to a public statistic, then builds a short chain. Present as an order of magnitude with a factor-of-two band, not a fake census count.
1. Annual US spend on meal-kit subscriptions
Object. Direct-to-consumer meal kits, US, $/year. Exclude grocery pickup and restaurant delivery.
Anchor. The BLS Consumer Expenditure Survey reports about 135.8 million consumer units in 2024 and average food-at-home spend of $6,224 per unit. That is the ceiling you must sit under, not the answer.
Chain.
- Consumer units: 136 million (round the BLS count).
- Share that ever buy a meal kit in a year: 4% (Ned: paid subscription is still a niche) → 5.4 million buyers.
- Average active months: 6 of 12 (churn and seasonal use).
- Boxes per active month: 3.
- Price per box: $60.
Spend: 5.4m × 6 × 3 × $60 ≈ $5.8 billion / year.
Sanity. Food-at-home aggregate is 136m × $6,224 ≈ $850 billion. A ~$6 billion meal-kit slice is under 1% of food-at-home — plausible for a niche. If you land near $80 billion, you sized grocery, not kits.
Say aloud. "Order of $5–7 billion, driven by penetration and boxes per month; food-at-home from BLS is the ceiling."
2. Athletic shoes sold in the US per year
Object. Pairs of athletic / lifestyle sneakers sold at retail, US, units/year. Exclude dress shoes.
Anchor. The Census Bureau estimated the US resident population at 340.1 million on July 1, 2024.
Chain.
- Population: 340 million.
- Share that buy at least one athletic pair per year: 60% (kids and active adults dominate; some adults buy zero).
- Pairs per buyer per year: 1.5 (one replacement plus some multi-pair buyers).
Volume: 340m × 0.60 × 1.5 ≈ 310 million pairs / year.
Sanity. That is roughly 0.9 pairs per person per year across the whole population — in the right ballpark for a category that includes running, training, and fashion sneakers. If you get 2 billion pairs, you counted every shoe category twice.
Say aloud. "Order of 300 million pairs, plus or minus a third, driven by pairs per buyer."
3. Active general-aviation aircraft in the US (stock)
Object. Active civil general-aviation fleet (including on-demand Part 135), stock, not hours. Exclude scheduled Part 121 air carriers.
Anchor. Build bottom-up, then check the FAA General Aviation and Part 135 Activity Survey.
Chain (pilot-side).
- US population: 340 million (Census, as above).
- Active private / commercial pilots as a share: rough 0.2% of population who hold and use a certificate → ~680,000 pilots (order of magnitude; many certificates are inactive).
- Share of those who are "active" in GA this year: 50% → 340,000.
- Active aircraft per active pilot: many pilots share club or rental aircraft — use 0.6 aircraft per active pilot.
Stock: 340,000 × 0.6 ≈ 200,000 aircraft.
Sanity. The FAA's 2023 GA survey puts active GA and Part 135 aircraft on the order of 214,000. A bottom-up ~200k that lands next to the survey is a pass. A answer of 2 million means you treated every pilot as owning a private jet.
Say aloud. "Order of 200,000 active GA aircraft; I would expect the FAA survey to be nearby."
4. Annual UK spend on private gym memberships
Object. Private gym and leisure-club memberships, UK, £/year. Exclude free outdoor exercise and one-off day passes.
Anchor. ONS mid-year estimates put the UK population near 68–69 million (mid-2023 about 68.3 million; later releases revise upward toward ~69 million for mid-2024). Use 69 million.
Chain.
- Population: 69 million.
- Adults 16+: ~80% → 55 million.
- Gym membership rate: 15% of adults → 8.3 million members.
- Average fee: £40 / month × 12 = £480 / year (budget chains pull the average down from premium clubs).
Spend: 8.3m × £480 ≈ £4.0 billion / year.
Sanity. £4 billion is about £58 per UK resident per year, or ~£70 per adult — believable for a minority membership product. If you get £40 billion, you assumed every adult pays premium dues.
Say aloud. "Order of £4 billion, driven by membership rate and monthly fee."
5. Annual India spend on packaged drinking water (PET bottles)
Object. Retail PET bottled water, India, Rs / year (or $ for the interviewer). Exclude water ATMs and large jar delivery if they agree.
Anchor. Use a population you can defend. India's census and UN estimates put the country near 1.4 billion; for interview math use 1.4 billion. Urban share is the lever — World Bank / UN urban data put India's urban share in the mid-30s percent in recent years; use 35% urban as a stated assumption.
Chain.
- Population: 1.4 billion.
- Urban: 35% → 490 million.
- Urban buyers of PET water in a year: 40% → 196 million people.
- Bottles per buyer per year: 50 (roughly one per week, with heavy users in the mix).
- Price per 1L bottle: Rs 20.
Spend: 196m × 50 × Rs 20 ≈ Rs 196 billion / year (~$2.3 billion at Rs 85 / $).
Sanity. Rs 196 billion is about Rs 140 per Indian per year nationwide — low as a national average, which is correct because rural PET penetration is thin. If you get Rs 2 trillion, you applied urban bottle rates to the whole country.
Say aloud. "Order of Rs 200 billion, almost entirely an urban story; rural jar and ATM water is out of scope."
What trips people on bank-style prompts
Stock vs flow. Prompt 15 is a stock. Prompt 19 is capacity that becomes a flow only after utilization. Mixing them produces machines × scans with no utilization term.
Value with no price. If they want $, state a placeholder price and keep going. Do not freeze waiting for a "correct" ASP.
Template panic. The unique fail on this page's territory is pasting US households × $100 onto a B2B, capacity, or emerging-market prompt. Change the first factor.
Wrong object. Bagged retail cement is not ready-mix. Meal kits are not DoorDash. Say the exclusion in the first sentence.
Practice this today
Pick five prompts from different structure groups above. For each: thirty seconds to name the structure and first cut, five minutes for the chain, one sentence for the sanity check. Then run ten timed reps on /drills/market-sizing or pull fresh stems from /tools/market-sizing-questions. Everything on CoachNed is open for seven days with no card; then $120 for a recruiting season or $49 a month.
When you want the long-form size with an assumptions table the interviewer can challenge cell by cell, switch to market sizing step by step. When the prompt is a pure count with no price, use guesstimate interview questions.
CoachNed is not affiliated with McKinsey, BCG, Bain, Deloitte, or any firm named in interview folklore.
Frequently asked questions
How many market sizing questions should I practice before interviews?
Enough to hit every structure type above cold — roughly twenty to thirty timed reps, not two hundred memorized TAMs. If you can open a random prompt and name stock, flow, value, or capacity in fifteen seconds, you are ready for first round.
Do interviewers expect an exact number?
No. They expect a transparent chain, clean units, and a band you would defend if challenged. An order-of-magnitude answer with a named driver beats a precise wrong object.
What is the difference between a market sizing question and a guesstimate?
Sizing usually wants a market in $ / year or units / year for a defined product and geography. A guesstimate is often a pure count ("how many piano tuners") with no price. Overlap exists; clarify the output units in your first sentence.
Should I start from supply or demand?
Pick one as the chain and use the other as the sanity check. Demand-side (households × usage) is usually clearer for consumer products; supply-side (capacity × utilization) is clearer for hospitals, factories, and fleets.
Where can I find more market sizing practice questions?
Use the bank on this page, then /tools/market-sizing-questions for fresh stems and /drills/market-sizing for timed scoring. For the full method, see market sizing step by step.
Sources
- New 2024 Population Estimates Show Nation's Population Grew by About 1% to 340.1 Million Since 2023 — US resident population anchor (July 1, 2024). Checked 2026-09-24.
- Consumer Expenditures — 2024 (BLS news release) — consumer-unit count and food-at-home spend for the meal-kit ceiling. Checked 2026-09-24.
- General Aviation and Part 135 Activity Surveys — CY 2023 (FAA) — active GA fleet sanity check for the aircraft stock size. Checked 2026-09-24.
- Population estimates for the UK: mid-2023 (ONS) — UK population anchor for gym spend. Checked 2026-09-24.
- Urban population (% of total) — India (World Bank) — urban-share assumption for India PET water. Checked 2026-09-24.