How many tons does an average cumulus cloud weigh?

How to get close to this number

Multiply volume by water content. A cumulus cloud is roughly a kilometre across in each dimension, which is a billion cubic metres, and it holds around half a gram of water per cubic metre. Volume times density gives a figure in the hundreds of tonnes.

The apparent paradox is the good part: something weighing hundreds of tonnes is floating. The resolution is in the explanation — the water is dispersed as microscopic droplets, and the cloud as a whole is less dense than the air beneath it. Weight and buoyancy are different quantities, and a heavy thing floats whenever it is less dense than what it sits in.

The droplet size is what makes the dispersion work. Cloud droplets are small enough that air resistance nearly balances their fall, so they descend at centimetres per hour rather than metres per second. When they merge and grow past a threshold, they stop being suspended and become rain — which is the whole of precipitation in one sentence.