As a meteorologist, I tend to think I'm pretty knowledgeable about the weather. Yet in all my years of studying the weather, this is a question that I have never been asked, nor heard posed.

At first thought, you might think that the weight of a cloud is... well, nothing, right? After all, they float in the air above us.

But clouds are made up of tiny particles (mainly water droplets) and all particles have to weigh something. So let's do some math.

Going back to physics class, mass = volume x density. Let's work in metric for now. First, let's figure out the volume of our cloud.

For this example, we'll consider a puffy cumulus cloud. Meteorologists have estimated the average cumulus cloud to be 1 kilometer. Considering that cumulus clouds have roughly the same length, width, and height , this would give us 1 cubic kilometer (1 km³), which equals 1 billion cubic meters (1,000,000,000 m³). That is very large!

Next, we need the density of the cloud. Scientists have worked out the water density of this type of cloud to be around 0.5 grams of water per cubic meter (g/m³).

1,000,000,000 m³ x 0.5 g/m³ = 500,000,000 g, which converted into pounds is about 1.1 million pounds. That's 550 tons of cloud!

But weight, er, wait... how can something that weighs so much float effortlessly above us?!

The answer goes back to our good ol' friend, density. The moist air of the cloud is much less dense than the dry air around it, so it floats!