# How Much Does a Cloud Weigh?

## Science Center Objects

I don't know anyone who is afraid to walk underneath a cumulus cloud because they are afraid it might fall on them. We don't think of clouds even having weight because they are floating. But, clouds are made up of a physical substance, water, and water is quite heavy, so clouds must have weight. We will explain this "paradox" to you if you read on.

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### How much does a cloud weigh?

We will use math instead of a giant weight scale to calculate the weight of a cumulus cloud.

Do you think clouds have any weight? How can they, if they are floating in the air like a balloon filled with helium? If you tie a helium balloon to a kitchen scale it won't register any weight, so why should a cloud? To answer this question, let me ask if you think air has any weight—that is really the important question. If you know what air pressure and a barometer are, then you know that air does have weight. At sea level, the weight (pressure) of air is about 14 ½ pounds per square inch (1 kilogram per square centimeter).

Since air has weight it must also have density, which is the weight for a chosen volume, such as a cubic inch or cubic meter. If clouds are made up of particles, then they must have weight and density. The key to why clouds float is that the density of the same volume of cloud material is less than the density of the same amount of dry air. Just as oil floats on water because it is less dense, clouds float on air because the moist air in clouds is less dense than dry air.

We still need to answer the question of how much a cloud weighs. To confuse things more, the weight depends on how you define it:

• The weight of the water droplets in the cloud
• The weight of the water droplets plus the weight of the air (mostly above the cloud, pressing down)

We're only going to look at the weight of the actual cloud particles. One estimate of cumulus cloud density is given at https://www.sciencealert.com/this-is-how-much-a-cloud-weighs, as a density of about 0.5 gram per cubic meter. A 1 cubic kilometer (km3) cloud contains 1 billion cubic meters.

Doing the math: 1,000,000,000 x 0.5 = 500,000,000 grams of water droplets in our cloud. That is about 500,000 kilograms or 1.1 million pounds (about 551 tons). But, that "heavy" cloud is floating over your head because the air below it is even heavier— the lesser density of the cloud allows it to float on the dryer and more-dense air.

The little cloud that could—but why? (Why does this cloud exist?)