How much does a cloud weigh?

A typical cumulus cloud (the most common cloud) is about 1 cubic kilometer in volume and 2 km above ground. Air density is estimated to be at about 1.007 kg/m3. The clouds (water droplets) are less dense and come close to 1.003 kg/m3 (which is also why they float). There are estimated to be 1,000,000 cubic meters of droplets in an average cumulus cloud.

A cumumus cloud weighs over a billion kilograms
The weight can be calculated using this equation (density by volume by a factor):

1.003 kg/m3x 1,000x 1 km3 = 1,003,000,000 kg

Which is over a billion kilograms of droplets or close to 2.2 billion pounds.

Assuming a blue whale is close to 160 (160,000 kg) tones in weight, a cumulus cloud weighs as much as 6,268.75 blue whales!