The cloud droplets of average size is only 1/2500 inch in diameter .
It is so small that it would take sixteen house to fall half a mile perfectly still air, and it does not fall out of moving air at all. Only when the droplet grows to a diameter of 1/25 inch or larger it can fall from the cloud. The average raindrop contains a million times as much water as a tiny cloud droplet to a size large enough to fall out is the cause of rain the other forms of precipitation. This important growth process is called coalescence.