Picture the puffiest, most harmless cloud you can. A fair-weather cotton ball drifting over a summer field. It weighs about 1.1 million pounds. That is roughly a hundred elephants, hanging silently over your head, not falling on you. So how much does a cloud weigh, and how does something that heavy just sit up there? It turns out to be one of the quietest magic tricks the sky performs.

A hundred elephants, give or take

A small cumulus cloud, the classic puffy kind, weighs around 1.1 million pounds, about 500,000 kilograms or 551 tons (USGS). UCAR puts it in friendlier terms: roughly a hundred elephants (UCAR Center for Science Education).

Getting to that number is almost suspiciously simple. A cumulus cloud carries about half a gram of liquid water in every cubic meter of air, and a typical one is roughly a kilometer on a side, which is a billion cubic meters. Half a gram times a billion is 500 million grams, or 500,000 kilograms of water (USGS). Bigger clouds run the figure up fast. A towering thunderstorm holds far more water than a fair-weather puff and weighs many times as much.

Why a million pounds of water doesn't drop

Here is the first part of the trick: that water isn't sitting in a bucket. It is shattered into millions of separate droplets, each one smaller than the width of a hair, with a radius of about 5 to 10 microns (Live Science).

A droplet that small barely falls at all. Its terminal velocity, the fastest it can drop, is only about 60 to 120 feet per hour (Live Science). That is slower than a snail. And while it creeps downward, the warm air rising up through the cloud, the updraft, pushes back and holds it in place (Scientific American). The droplets really are falling on you. Just at the pace of dust drifting in a sunbeam.

The cloud is lighter than the air around it

There is a deeper reason, and it is the one that makes the elephants stop being scary. Spread half a million kilograms of water across a whole cubic kilometer of sky and it barely registers. The dry air filling that same cubic kilometer weighs about a billion kilograms, a thousand times more than the water floating in it (Scientific American).

A cloud, in other words, is mostly air. And the warm, water-laden air inside it is actually a touch less dense than the clear dry air around it, so the whole parcel floats, the way a cork rides on water (USGS). The weight was never really the problem. Weight only matters next to whatever is holding it up, and the sky does a lot of holding.

When the droplets finally give in

So when does all that water come down? When the droplets stop being tiny. Inside the cloud they collide and merge into bigger drops, and once a drop grows heavy enough to beat the updraft, it falls out of the bottom as rain (UCAR Center for Science Education). That is why a cloud can hang there all afternoon and then, fairly suddenly, start to pour. The amount of water didn't change. The packaging did.

It quietly rewrites what you're looking at. That smudge of white you ignore on a nice day is a flying lake, held up by nothing but the slowness of small things and the patience of warm air. The next time one drifts overhead, you can tell yourself, accurately, that a hundred elephants just passed by without making a sound.

Keep wondering: all that suspended water eventually has to come down, which is why it rains; those same tiny droplets and the air around them scatter sunlight, part of why the sky is blue; and when that water finally freezes it pulls a trick of its own, namely why ice floats.