For water droplets to be classified as rain, what is the minimum diameter they must reach?

For water droplets to be classified as rain, they must reach a minimum diameter of 0.5 mm. This size is significant because droplets smaller than this typically evaporate before they can reach the ground and are instead classified as mist or drizzle. The process that allows droplets to grow to this size involves condensation and collision-coalescence within clouds, where smaller droplets combine to form larger ones. Once they reach the 0.5 mm threshold, these droplets can fall to the ground as precipitation. This measurement is crucial in meteorology for distinguishing between different forms of precipitation based on droplet size.