In science we learn that one question often leads to another, or several others. Before we can discuss raindrop sizes, we must understand what a raindrop is.
Condensation occurs when the water vapor wraps itself around the tiny particles.
However, these droplets are too light to fall out of the sky. Picture a huge room full of tiny droplets milling around. As it falls it eats up even more droplets. We can call the growing droplet a raindrop as soon as it reaches the size of 0.5mm in diameter or bigger. If it gets any larger than 4 millimeters, however, it will usually split into two separate drops.