This USGS article: "Raindrops are Different Sizes" assures:
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.
However, this article in the spanish newspaper El Pais: "Alien raindrops are like those on Earth" is contradictory:
The average diameter that a raindrop can have on Earth is 11.18 millimeters
A commenter on the news article says the article is wrong, but he says a raindrop can reach 6 milimeters and not 4.
The data for the average size of the raindrops on earth is wrong, since they rarely exceed 6 mm in diameter (equivalent). From this size, the drops become unstable and tend to divide into a pair of smaller drops.
What is the maximum size that a drop of rainwater can reach before spliting into two separated drops?