2QUESTION 2 OF 3
Answer & explanation
The official answer, with Fermi’s reasoning step by step.
Answer & explanation
Official answer
750,000,000
people
How to estimate it
Fermi’s official “Napkin math”
The easiest place to start is the world's population, about 8 billion. How many of them have blue eyes? Not many, brown dominates almost everywhere. Maybe 1 in 10.
- World population
- 8,000,000,000
- Have blue eyes
- ≈ 1 in 10
- 8B ÷ 10
- ≈ 800,000,000
Rounded assumptions may give a slightly different estimate. The official answer above is the game’s reference value.
Source calculation & reference
- World population (2026)
- ≈ 8.3 billion
- Share of people with blue eyes
- ≈ 8–10%, take 9%
- 8.3B × 9%
- ≈ 750,000,000
Reference cited by Fermi: Genetics-based population estimate widely cited by eye-color researchers (Medical News Today, World Atlas, World Population Review)
How close was your guess?
Your comparison will appear here.
Compare by ratio: divide the larger number by the smaller one. The closer to 1×, the better.