What Is Fermi?
Fermi is a daily estimation game built around questions that are difficult to answer from memory but possible to approximate with reasonable assumptions. Each day gives you three numerical questions. You get one guess per question, and the goal is to land as close to the real answer as possible. Typical Fermi questions ask about quantities such as: - How many iPhones have been produced since 2007? - How many Oreos are eaten in the US each day? - How many steps does a mail carrier walk in a year? - How many golf balls could fit inside a car? You are not expected to know these numbers exactly. The intended approach is Fermi estimation: break a difficult quantity into smaller things you can estimate, do some quick arithmetic, and aim for the correct scale.
The Core Twist: Factor-Based Scoring
Fermi does not score you by ordinary numerical distance. Instead, it measures how many times larger or smaller your guess is than the real answer. If the true answer is 1,000: - Guess 1,000 → 1× - Guess 2,000 → 2× - Guess 500 → 2× - Guess 10,000 → 10× - Guess 100 → 10× Lower is better, and 1× is a perfect estimate. This matters because Fermi questions often involve very large numbers. Missing a billion-unit answer by a few million should not be treated the same way as missing a thousand-unit answer by a few million. Your final daily score is the average factor across all three questions.
How to Play Fermi
1. Read the Question and Identify the Quantity Start by making sure you understand exactly what is being asked. For example: How many cups of coffee are consumed in a country each day? Important details include whether the question asks for a daily or yearly total, individuals or households, and a count or a monetary value. Unit mistakes can be much more damaging than imperfect assumptions. 2. Break the Problem Into Smaller Estimates Rather than guessing one huge number directly, build a simple model. For the coffee example, you might use: population × share of coffee drinkers × cups per drinker per day Suppose you estimate: 50 million people × 60% × 2 cups That gives: 60 million cups per day The individual numbers do not need to be exact. You are trying to get into the right numerical neighborhood. 3. Use the Built-In Calculator and Lock In One Guess Fermi includes a calculator, so you can work through rough multiplication and division without leaving the game. Enter your final number and lock it in. There is no second attempt for that question, so do a quick sanity check before submitting. 4. Review the Answer and Your Factor Fermi immediately reveals the reference answer and tells you whether your estimate was too high or too low. You also see your factor error. For example: Your guess: 12 million Answer: 8 million Result: 1.5× too high The game also shows how your estimate compares with other players. 5. Study the Napkin Math and Continue After each question, Fermi provid
A Realistic Fermi Example
Imagine the question is: How many slices of pizza are eaten in a city each day? You probably do not know the statistic directly. Start with population: 8 million residents Assume the average resident eats roughly two slices per week: 8 million × 2 = 16 million slices per week Convert to days: 16 million ÷ 7 ≈ 2.3 million per day You might increase that slightly to account for tourists and commuters and submit: 2.6 million Even if every assumption is somewhat wrong, this structured estimate is much more defensible than entering a completely arbitrary number.
Strategy Tips for Better Fermi Scores
Find the Order of Magnitude First Before worrying about whether the answer is 42 million or 57 million, decide whether it is more likely to be: thousands millions billions or trillions Being slightly inaccurate within the correct scale usually produces a much better Fermi score than performing precise arithmetic on a fundamentally wrong magnitude. Use Familiar Reference Points Anchor difficult questions to quantities you already understand. Useful reference points include: - World population - Population of major countries - Days in a year - Hours in a day - Approximate human lifespan - Typical household size - Common speeds and distances - Rough prices of everyday goods You do not need a huge collection of memorized statistics. A few reusable anchors can solve many different questions. Turn Questions Into Multiplication Chains Many Fermi problems can be rewritten as simple structures such as: people × activity per person locations × activity per location rate × time volume ÷ volume per object population × percentage × frequency This is usually easier than trying to recall the final number directly. Keep the Model Simple Adding more assumptions does not automatically improve an estimate. A chain with ten uncertain inputs gives you ten opportunities to make a bad assumption. Look for the shortest reasonable route to the answer. For example, estimating annual cinema tickets might only require: population × average cinema visits per person per year You probably do not need to mo
