How many piano tuners are in Chicago? How many tennis balls fit in a school bus? Master the art of order-of-magnitude estimation.
Estimation
Order of magnitude
Quick Math
Back of envelope
Logical Breakdown
Step by step
Consulting
Interview prep
Enrico Fermi famously estimated the strength of an atomic bomb blast by dropping paper scraps. Now it's your turn.
Estimate the answer to the nearest Order of Magnitude.
Fermi Estimation Duel is a problem-solving game that trains you to make reasonable estimates for seemingly impossible questions. Named after physicist Enrico Fermi, these estimation skills are tested in consulting, product management, and tech interviews.
The game presents varied estimation challenges and pits your reasoning against benchmarks. You develop the structured thinking and comfortable uncertainty that impress interviewers and help in real-world decision making.
The game covers diverse estimation domains:
Question Types: • Market Sizing: How large is the market for X in India? • Counting: How many Y are there in a city/country? • Rate Questions: How much Z happens per day/year? • Capacity: How many people/things can fit in a space? • Revenue/Cost: What might a business earn or spend?
Duel Mode: Compete against AI or previous players with your estimates.
Get a seemingly impossible-to-answer estimation question.
Decompose into smaller, estimable components.
Estimate each component based on knowledge and logic.
Combine estimates and compare your answer.
Fermi Estimation develops valuable reasoning skills:
Problem Decomposition: Breaking complex questions into manageable pieces.
Numerical Reasoning: Working with orders of magnitude and quick calculations.
Assumption Making: Choosing reasonable values when data is unavailable.
Sanity Checking: Validating answers against known references.
Comfortable Uncertainty: Working productively even without complete information.
Estimation skills shine in specific assessments:
Consulting Interviews: Market sizing is a core case interview component.
Product Management: PMs constantly estimate TAM, user metrics, and impact.
Tech Guesstimate: Companies like Google and Microsoft ask system estimation questions.
Business Case Competitions: Quick sizing skills help in limited-time cases.
Fermi Estimation benefits strategic thinkers:
• Consulting Aspirants: Master the market sizing questions firms love • PM Candidates: Build the estimation skills PM interviews test • Tech Interviewees: Prepare for guesstimate-style questions • Business Students: Develop practical business intuition • Anyone Seeking Quick Thinking: Sharpen numerical reasoning
This game applies estimation research:
Decomposition: Breaking problems down produces more accurate estimates.
Anchor Numbers: Building reference libraries improves estimation accuracy.
Calibration: Regular practice improves estimation confidence calibration.
Order of Magnitude: Focusing on magnitude rather than precision reduces errors.
Build a mental library of useful anchor numbers (populations, prices, rates)
Always state your assumptions explicitly - that is what interviewers want to see
Check your final answer against reality - does the magnitude make sense?
Round numbers freely - 10 million is easier to work with than 9.7 million
For market sizing, use population → % relevant → frequency × price formula
