thinking-fermi-estimationlisted

# Fermi Estimation ## Overview Fermi estimation, named after physicist Enrico Fermi, is the art of making reasonable estimates for quantities that seem impossible to know without direct measurement. By decomposing a question into factors you can estimate, then multiplying, you often get surprisingly accurate order-of-magnitude results. **Core Principle:** Break the unknown into known (or estimable) pieces. Even rough estimates combine to reasonable accuracy due to errors canceling out. ## When to Use - Capacity planning ("How much storage will we need?") - Cost estimation ("What will this infrastructure cost?") - Market sizing ("How many potential users exist?") - Feasibility assessment ("Is this even plausible?") - Sanity checking ("Does this number make sense?") - Interview questions ("How many piano tuners in Chicago?") - Quick prioritization ("Is this worth pursuing?") Decision flow: ``` Need a number you don't have? → yes → Can you measure it directly? → no → FERMI ESTIMATE ↘ yes → Measure ↘ no → You might not need it ``` ## The Fermi Process ### Step 1: Clarify What You're Estimating Be precise about the quantity: ``` Vague: "How big is the market?" Precise: "How many SaaS companies with 50-500 employees in the US would pay $1000/month for our product?" ``` ### Step 2: Decompose into Estimable Factors Break into pieces you can estimate: ``` Storage nee