Cats have whiskers in more places than just their cheeks, though that is the most common place. They also have them on their chins, eyebrows, and legs. The whiskers on their cheeks are the longest and most noticeable with 8-12 on each cheek. Occasionally whiskers will fall out and they are completely replaced within 2-3 months.
The whiskers grow to the length of the widest part of the cat’s body, normally their shoulder or hip span. They use their whiskers to gauge if they’ll be able to fit through openings. When a cat ducks its head into a space, it is actually seeing whether it’ll fit its body through the space by seeing how much space its whiskers have.
If the whiskers bend or move, then the cat knows it won’t be able to fit through the space. They can also feel air movement flow through their whiskers. This helps them gauge distances and changes in air flow so they don’t run into things.