Rats generally have between 6 and 12 babies (called pups or kittens) in their litters. Female rats can be pregnant for anywhere from 21 to 28 days.
The number of pups in a rat's litter increases the more litters she has, and then it decreases again when her fertility wanes. The maximum amount of pups a rat can have in a litter is in the mid twenties, but 6 to 12 is more normal. The pups are blind, deaf and hairless at birth, and they rely on their mother's milk for nourishment. They are usually weaned by the time they are 21 days old.