When you look up at clouds in the sky, you typically think of them as fluffy and light, right?
Turns out, clouds are HEAVY! The average cumulus cloud weighs over a million pounds! Which presents a couple of questions: 1) how do clouds remain aloft, and 2) how do you weigh a cloud?
The answer to the first question is that clouds are constantly falling toward the earth. But they’re also constantly changing–condensing and evaporating. That, combined with air circulation, works to keep clouds in a generally skybound location.
As for the second question, one article explains: “Cloud droplets are spherical and the density of water is known, so the number and size of the droplets can be measured in a known volume (usually one cubic centimetre). Multiply this by the total volume of the cloud and you can calculate its weight.” So it doesn’t involve a giant scale, it just involves a small scale and some math!
You can read more about the science of clouds (which is called nephology) at Wikipedia!