A Cloud Weighs More Than You Might Think

Posted January 13, 2011 by admin in Fun Facts

Staring at the sky yesterday made me ponder something. Clouds are fluffy looking, float above our heads in the sky, and contain mostly water vapor. They seem like they should weigh next to nothing, right?

How much do they weigh?

Clouds can vary widely in size, shape, and density. This means there is no way to accurately gauge weight, but we can do a rough estimate. After a bit of research, I discovered clouds are substantially heavier than I previously thought.

The density of clouds varies quite a bit, from about 1/10 gram per cubic meter to over 5 grams per cubic meter. This makes it quite hard to come up with an “average” cloud volume, as this varies even more widely than the actual water content.

To get at least a rough order-of-magnitude estimate, we have to plug in some averages into our equation, making this far from scientifically accurate. If we model our cloud as a sphere of say, 1 kilometer radius, that gives a volume of about 4 billion cubic meters. Then if we use 1 gram per cubic meter as a “representative” water content, we get an estimate for the mass of the cloud of 4 million kilograms, or 8,818,490 pounds. That’s 37 fully grown blue whales.

A good sized cumulonimbus cloud (also known as a thunderhead) might be ten kilometers tall, with a base ten kilometers in diameter. Estimating that, we come up with a volume of 785 billion cubic meters per cloud. This gives us a mass of roughly four billion kilograms per cloud. That’s 10,000 747 jets.

If one fell on us, it would … just get real foggy. Luckily, weight isn’t the same as mass. A cloud put on a scale wouldn’t weigh anything.

Fun fact: Roll Clouds (pictured at the top of this entry)

A roll cloud is a low, horizontal tube-shaped arcus cloud associated with a thunderstorm gust front, or sometimes a cold front. Cool air sinking air from a storm cloud’s downdraft spreads out across the surface with the leading edge called a gust front. This outflow undercuts warm air being drawn into the storm’s updraft. As the cool air lifts the warm moist air water condenses creating cloud, which often rolls with the different winds above and below (wind shear).