They seem weightless, floating around in the sky. By virtue of being in the sky without crashing down, they have to be quite light… Right? But dismissing the weight of a cloud as ambiguously “light” seems boring, and is probably untrue. You looked up the question to see if it was or not, after all. So how much do clouds weigh?
Weighing Clouds
So before we weigh clouds, we have to figure out how we’re even going to weigh clouds in the first place.
Luckily, someone much smarter than us named Margaret “Peggy” LeMone from the US National Center for Atmospheric Research figured it out. There are some baseline things you need to know before you start using the power of math to figure out how much clouds weigh. You need to know how dense they are and how much space they take up (their volume). If you took high school science classes and remember, things might all be coming together right about now. Density is equal to mass over volume. If we know density and volume then we know cloud density multiplied by its volume will give us the cloud’s mass.
Measurements
The average cumulus cloud (the cloud you probably think of when someone says “cloud”) fills up about 1 cubic kilometer (or about 0.24 cubic miles if you’re not metric). Which is a box a kilometer tall, wide, and long. That’s a billion cubic meters. While you can’t really measure how tall a cloud is yourself, you can approximate their length or width yourself if you were really feeling like it. LeMone did it by driving underneath clouds while the Sun was directly above them. She just watched the shadow and her odometer.
Now figuring out cloud density. You don’t have to measure anything to figure this out. Clouds are mostly liquid water and ice. Also now you can correct anyone who just says clouds are water vapor. As an aside if you’re wondering how that works, it works the same way you get water droplets on the outside of your cold water bottle. There are tons of tiny particles in the sky, dirt, smoke, salt from the sea. Clouds form at an elevation where it’s cold enough for evaporated water to turn to liquid or freeze again. You know this if you’ve been on a plane–you’d have seen frost accumulating on the windows. Water condenses on the little particles, and bam, slam, welcome to the jam. You’ve got a cloud.
The measured water density of the average cumulus cloud is about 0.5 grams of water per cubic meter (500,000,000 grams per cubic kilometer). Water density is different from different clouds, the high altitude and wispy cirrus clouds contain much less water.
So math time, we know density, we know volume. Since the average cumulus is 1 cubic kilometer, we actually don’t have to do… Much math at all. It’s just 500,000 kilograms or 1.1 million pounds.
See if you can’t identify more cloud types here.
