Question How much does a cloud weigh?

Answer

Scientists have a method for calculating a cloud’s weight. It starts with figuring out the approximate size of the cloud.

Black and white image of a cloud billowing up in the sky — Clouds. 1942. FSA/OWI Collection, Library of Congress Prints & Photographs Division.

What exactly is in a cloud?

Before we can estimate a cloud’s weight, it helps to understand just what a cloud is made of. Here on Earth, the air around us is has invisible water vapor in it. When that water vapor cools and condenses into liquid water droplets or solid ice crystals, visible clouds form. So, clouds are made of water in different states of matter, and that is primarily what contributes to a cloud’s weight. Also, it’s good to keep in mind that the density of water changes depending upon the air temperature. As the temperature changes, the molecules of water will pack closer together or move farther apart. That will change how many molecules fit in a gallon of water and so a gallon of water will vary somewhat in weight.

How many gallons of water might be contained in a typical cloud?

There are methods for estimating the weight of a cloud by estimating the weight of water in it. Of course, no one knows for sure the exact volume of water in a cloud, but there are equations to help pin down an estimated sum. To do this, we must first measure the cloud.

A wide angle shot shows distant islands in a flat mirror-like sea which reflects clouds — Which way is up? A mirror-smooth sea reflects cumulus clouds on a still morning in the Keys. 2018. NOAA Photo Library.

Measuring a cloud

Yes, measuring a cloud! In The Complete Weather Resource, Phillis Engelbert gives an explanation of how to estimate the weight of a cloud (vol. 1, p. 83). This source provides an equation on how to determine the volume of a cloud by first measuring it. Since meteorologists use the metric system, the example will use meters.

Engelbert states that it is easier to measure small to medium cumulus clouds since they have similar values of length, width, and height. To get the length of the cloud you measure the shadow. If it is a kilometer long, that equals 1,000 meters. Then estimate the cloud’s width and height.

Photo of tree tops and a clear blue sky with a single small white cloud. — Clouds: Why Does This Little Cloud Exist? USGS Multimedia Gallery.

Determining volume and weight

Suppose that the cumulus cloud you are measuring is about 1,000 meters long and about equal in height and width (1,000 meters for each dimension). To find the cloud’s volume multiply width by length by height: 1,000 meters X 1,000 meters X 1,000 meters. This equals 1,000,000,000, or 1 billion cubic meters.

Then multiply the volume by the weight of water within 1 cubic meter of cumulus cloud, which has been calculated as .5 gram. One billion cubic meters times .5 gram per cubic meter equals 500 million grams. Thus, the cloud weighs about 500,000 kilograms!

A photograph of scattered small clouds above the ocean with indistinct shapes on the ocean surface that may be cloud shadows or islands — Cumulus, sun glint, and cloud shadows – or are those coastal islands? 1967. NOAA/AOML/Hurricane Research Division, NOAA Photo Library.

You can convert this number to gallons of water. One way to is to convert the kilograms into pounds. One kilogram is the same as approximately 2.2 pounds, so 500,000 kilograms will equal about 1,100,000 pounds. According to the CRC Handbook of Chemistry and Physics, 68th Edition table, “Weight of One Gallon of Water (U.S. Gallons)”, on p. F-2, a gallon of water in air weighs between 7.99 and 8.34 pounds depending upon the temperature. Using the upper amount, 8.34 pounds divided into 1,100,000 pounds, equals 131,894 gallons. So, the estimated amount of water in a cumulus cloud which is 1,000 meters in length would be about 131,894 gallons.

Knowing how much a cloud weighs might make you wonder how it can be so heavy and still stay floating up in the sky. Although clouds are heavy, with thousands or even million of gallons of water, they stay up in the sky because the individual liquid water droplets and solid ice crystals are small enough to float on even the slightest breeze. Should the droplets or crystals clump together though… down they can come — as rain and snow!

Illustration shows three old men sitting on a stonewall watching the clouds form beautiful ballerinas dancing a ballet. — The Cloud Ballet . Gordon Ross. 1911. Library of Congress Prints & Photographs Division.

Published: 10/27/2023. Author: Science Section, Library of Congress

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