Question: There is one gallon of water in every cubic mile of what
Answer: Fog
The statement “There is one gallon of water in every cubic mile of fog” refers to the water content of fog. Let’s break it down:
Why is it so low?
- Fog is mostly air: It’s basically a cloud at ground level made up of tiny suspended droplets.
- Very low water content: Fog usually has only 0.05 to 0.5 grams of water per cubic meter (liquid water content).
Conversion to Gallons per Cubic Mile
1 cubic mile ≈ 4.17 trillion cubic meters. If we take a very light fog with minimal water content, the total amount of condensed water can be as little as 1 gallon per cubic mile. This shows how thinly spread the water droplets are in fog.
In short: Fog may look dense, but it’s mostly air. The liquid water is so spread out that a cubic mile of fog might contain only about one gallon of water.
Why is this surprising?
Because fog looks thick, yet the actual liquid water volume is tiny — the droplets are extremely fine (often 10–15 microns in diameter).
Fun fact: Even if a whole city is covered in fog, the total water may only fill a few bathtubs!
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