A cloud is made of tiny droplets.

A typical cloud droplet is about 0.02 mm across.

A typical raindrop is about 2 mm: 100 times wider.

Volume grows with the cube: 100 × 100 × 100 = 1,000,000.

A bigger drop falls faster, so it sweeps up smaller ones.

Fall speed grows with the square of the radius.

10 µm radius: 1.2 cm/s. 20 µm radius: 4.8 cm/s.

A 2 mm raindrop falls at about 5.6 m/s.

Over 1 km: about 3 minutes for the raindrop, 23 hours for the droplet.

Updrafts hold the small droplets up.

Droplets join until they are too heavy to stay up.

Rain is millions of droplets, joined and falling.