How Big Do Pet Rats Get?

Rats are relatively small animals when they are born, being one to two inches long. However, they begin to grow significantly after about a week. Their eyes and ear canals will open up, and the fur will start to show. By the time they reach 15 days, their eyes will be fully open and their bodies will fill up considerably. As a result, they will be much larger and more active.

The average adult rat is nine to eleven inches long, with a tail that can grow up to twenty inches. Their weight ranges from a few grams to more than two pounds. Rats can fit through tight spaces; they can fit through an opening the size of a quarter. For this reason, they’re best kept in separate cages.

Rats can reach sexual maturity at five to eight weeks of age, while males typically reach this age much later, between 10 and 12 weeks. Females usually go into heat for a period of twenty-four hours every four or five days, and can seem restless and agitated during this time. They are highly susceptible to breeding, so you should separate them as soon as they reach sexual maturity.