Estimation and market sizing interview questions
Estimation questions ask for a number you can’t look up, such as how many dentists there are in the US. The number matters less than the route to it: a clear equation, round assumptions with reasons, and a check.
Below: what the round tests, the method in short, and 25 practice questions, each with a first move and the outline of a strong answer. All free, no sign-up.
What the interviewer is scoring
- Whether you say the equation before any number goes into it.
- Whether each assumption comes with a one-line reason.
- Whether you check the answer by a second route and name the assumption that moves it most.
Watch a mock interview from this round
Grace’s first try, Ava’s pushback, then the stronger answer with its scorecard. The question: How many gas stations are there in the US?
Read what Ava and Grace say
- Ava:
- I'm Ava. Today I'm interviewing Grace, on counting gas stations.
- Grace:
- I'm Grace, a PM candidate. I dread estimation.
- Ava:
- Grace, here's an estimation question. How many gas stations are there in the US?
- Grace:
- Hmm. A lot. Maybe a million? Yeah, I'll say a million.
- Ava:
- A guess gives me nothing to grade. Show me the route. Try again.
- Grace:
- To clarify, I'm counting retail gas stations in the US today. Stations, not pumps, and not chargers. My equation is fill-ups per day divided by fill-ups one station handles per day. Now the numbers, each with a reason. About 250 million cars, since there are about 260 million adults and most have one. One fill-up a week, since a tank lasts about 300 miles and people drive about 250 miles a week. So 250 million divided by 7 is about 36 million fill-ups a day. A station has about 8 pumps, since the usual layout is two islands of four. A pump is busy maybe four hours a day at ten cars an hour, so 40 cars. 8 times 40 is 320, call it 300 per station. 36 million divided by 300 is 120,000 stations. Second route, from supply. The US has about 20,000 towns and cities. Small ones have one or two stations and big ones have hundreds, so say 5 on average. That is 100,000, so the two routes agree within twenty percent. The assumption that moves it most is cars per pump. At 80 a day, the answer halves to 60,000.
- Ava:
- That I can grade. A reason for every number, and a second route. That would score well.
The method in short
Estimation: the five-step estimate
- ClarifyPin down the unit, the place, the time period and what counts.
- StructureSay and write the equation before any number goes in.
- AssumeA round number for each part, each with a one-line reason.
- CalculateMultiply out loud, round as you go, and give the answer to one or two significant figures.
- CheckTest it from a second route (supply side, per person, an analogy) and name the assumption that moves it most.
Example
Weekday bike-share rides in a fictional city of 1 million: 1 million × 2% who ride × 2 rides each ≈ 40,000; check: 5,000 bikes × 8 rides a day ≈ 40,000. All round numbers, chosen for easy arithmetic.
Most common mistake
Multiplying numbers as they occur to you before the equation is set, then skipping the check, so a tenfold error goes unnoticed.
25 estimation and market sizing questions to practice
Pick one, answer it out loud on a timer, then open its page to compare with the outline. Start with the warm-ups if this round is new to you. Want a score? Paste your answer into the free answer grader, or answer it out loud with Ava.
Warm-up questions (6)
- How many dentists are there in the US?First move: Go from demand: how many dental visits Americans make each year, and how many visits one dentist can handle.
- How many smartphones are sold in the US each year?First move: Use a replacement-cycle approach: people who own smartphones divided by how many years they keep one.
- How many hours of video does the average US adult watch in a year?First move: Split by type: TV, streaming and short-form video on phones. Estimate a daily figure for each, then multiply by 365.
- How many diapers are used in the US in a year?First move: Count children in diapers, then multiply by changes per day and days per year.
- How many cups of coffee does an office of 500 people go through in a week?First move: Estimate the share of people who drink coffee at work and how many cups each drinks a day.
- How many hours does the average US commuter spend stuck in traffic each year?First move: Define 'stuck' first, such as time beyond a free-flowing trip, then estimate the delay per commute and multiply by commuting days.
Standard questions (14)
- How many gas stations are there in the US?First move: Pick a demand-side path: estimate how many fill-ups US drivers need each day, then divide by how many one station can serve.
- How many tennis balls are sold in the US each year?First move: Segment buyers. Regular players, casual players, clubs and dog owners all buy tennis balls at very different rates.
- Estimate the annual revenue of a busy coffee shop in a downtown area.First move: Build it bottom-up from customers per hour and average ticket, split by time of day, because a morning rush looks nothing like 3 p.m.
- How many Uber rides happen in New York City on a weekday?First move: Start with the population of the city and the share of residents and visitors who take a ride-hail trip on a typical weekday.
- How many emails are sent in the US every day?First move: Separate personal, work and automated emails. Automated messages such as receipts and marketing likely outnumber the ones people write.
- What's the market size for dog-walking apps in the US?First move: Define market size as annual spending, then go from dog-owning households to the share that pays for walks.
- How many pizzas are ordered in the US on Super Bowl Sunday?First move: Start with households watching the game and the share that hosts or joins a gathering, then estimate pizzas per gathering.
- How many wedding photographers are there in the US?First move: Go from weddings per year to how many weddings one photographer can shoot in a year.
- Estimate Netflix's annual subscription revenue in the US.First move: Estimate paying US households, then multiply by an average monthly price across plans.
- Estimate the number of Google searches made worldwide per day.First move: Start with internet users worldwide, then estimate searches per user per day, adjusting for regions where Google is not the main engine.
- How many elevators are there in Manhattan?First move: Segment buildings by height, because a five-story walk-up and a sixty-story office tower have very different elevator counts.
- Estimate the US market size for meal-kit subscriptions.First move: Pick a top-down path from households that cook at home and can afford meal kits.
- Estimate the annual revenue of a city parking garage.First move: Count spaces, then estimate how full the garage is and at what price, separately for weekdays, evenings and weekends.
- How many drivers would a new ride-sharing service need to launch in Austin?First move: Turn expected demand at peak into drivers needed, since peak hours, not daily averages, set the fleet size.
Stretch questions (5)
- Estimate the storage needed for one day of YouTube uploads.First move: Break it into hours of video uploaded per day times storage per hour, then account for multiple quality versions and backups.
- Estimate how many people are on flights over the US right now.First move: Start with flights in the air at a given moment, then multiply by average passengers per flight.
- Estimate how many public electric vehicle chargers California would need by 2030.First move: Go from expected EVs on the road to charging demand, then subtract home charging to find what public chargers must cover.
- How much would it cost to repaint every yellow school bus in the US?First move: Estimate the number of buses first, then cost per bus from paint, labor and time off the road.
- How many messages per second does a large messaging app handle at peak?First move: Go from daily active users to messages per day, then convert to an average per second and multiply by a peak factor.
Common questions about this round
How do I answer a market sizing question?
In five steps. Clarify the unit, the place and the time period. Say the equation before you fill it in. Give a round number for each part, with a reason. Multiply out loud and round as you go. Then check the result from a second direction, such as the supply side, and say which assumption would change it most.
Do I need to memorize numbers for estimation questions?
Only a handful of round ones, such as a country’s population and its number of households. The rest you reason out. Interviewers accept any sensible round number when you say where it comes from.
How accurate does my estimate need to be?
The right order of magnitude is enough. Give the answer to one or two significant figures and name the assumption it depends on most. A clear route to a rough number scores higher than a precise number nobody can follow.
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