Best Guess · Puzzle #2 · Thursday, October 1
Best Guess: the answers
Four questions, each with one true number. Here they are with their answers, how to reason each one out, and where the number comes from. Play today's Best Guess.
1. How many trees are there on Earth?
The answer: about 3 trillion. That is roughly ten times more than earlier estimates, though the study also found tree numbers have fallen by nearly half since the start of human civilization.
Napkin math: Forests cover roughly 40 million km² of land; guess how many trees stand on a typical hectare and multiply up.
Source: Nature (via Europe PMC), Mapping tree density at a global scale
2. How many flights does the FAA's air traffic system handle on an average day?
The answer: more than 44,000. Those flights carry more than 3 million airline passengers every day.
Napkin math: About 3 million airline passengers a day at roughly 100 per flight is 30,000 airline flights, plus cargo, private and military flights.
Source: Federal Aviation Administration, Air Traffic By The Numbers
3. How many of your cells does your body replace every day?
The answer: about 330 billion. Close to 90% of the cells replaced each day are blood cells.
Napkin math: Your body has about 30 trillion cells; if the average one lasts a few months, divide to get a daily turnover.
Source: Nature Medicine (via Europe PMC), The distribution of cellular turnover in the human body
4. How many domain names (.com, .org, country codes and all others combined) were registered worldwide in mid-2026?
The answer: 401.6 million. Registrations grew by 29.9 million, or 8.1%, over the previous year.
Napkin math: Hundreds of millions of businesses plus a long tail of personal sites and parked names, with many owners holding several domains each.