Your guess
How much water does a cumulus cloud of 1 km³ hold?
Worked out
500tonsof water in a one-cubic-kilometer heap cloud
In one cubic meter of heap cloud floats about half a gram of water. A cubic kilometer holds a billion cubic meters. That makes 500 million grams – about 500 metric tons of droplets.
The air weighs far more
Near the ground, a cubic kilometer of air weighs well over a million metric tons – more than two thousand times as much as the cloud's water. The water is just a tiny extra.
Why it floats
Cloud droplets are tiny, usually two to ten thousandths of a millimeter. As long as the air in the cloud rises faster than the droplets sink, they stay up. Only when they merge into drops too heavy for the updraft does it rain.
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