Clouds and Swimming Pools and Stuff

I love math, but normally I don’t set out to do mathematical calculations at 6 am. Still, I ended up doing so this morning when I took this question: If all the water in a typical backyard swimming pool were to become a cloud, how big would that cloud be?

It should be pointed out up front that a “typical backyard swimming pool” is entirely subjective. Pools can and usually are various shapes and sizes. There really isn’t such a thing as a ‘typical’ pool. That said, and in order to answer this question, a couple of things should be explained. First, the amount of water in a cloud is identical to the amount of water in the air around the cloud. A cloud is visible simply because the temperature in that area has caused the water vapor to condense into either droplets of rain or crystals of ice, depending on the temperature.

For those who don’t know, the volume of water inside of a cloud is very close to one-millionth of the volume of the cloud. This is 0.0001%. So a small cloud (‘small’ is also subjective) that measures 1,000 feet by 3,000 feet by 900 feet would have a volume of 2,700,000,000 cubic feet (1,000 times 3,000 times 900). This means that the cloud would hold 2,700 cubic feet of water, which is a millionth of 2,700,000,000. There are 7.48 US gallons of water in a cubic foot of water, so this example small cloud would hold 20,196 gallons of water. Now the answer to the question can be figured out.

An in-ground pool that measures 20 feet by 40 feet by 5 feet deep holds about 30,000 gallons of water. This is roughly a third again more water than in the cloud we used as an example. So if this pool was used as a typical pool, the cloud it would produce would be about a third larger than 1,000 feet by 3,000 feet by 900 feet. In fact, the cloud would measure slightly smaller than 3,350 feet by 900 feet by 1,000 feet.

What is amazing is how much all of that water, and thus the cloud, would weigh. The weight of water varies according to the temperature of the water and the pressure, however, a reasonable estimate would be 8.35 pounds per US gallon. That little cloud would weigh 250,500 pounds; over 125 tons! Clearly, clouds weigh more than it looks like they would.

Incidentally, the cloud in the picture is about the size of what was used in the example.