How Large Do Rats Grow?
WouterRats can grow to be quite large, and while the average rat is only five inches long, some can grow as large as 20 inches. Common brown rats weigh about one pound and are about the same size as pet rats. A rat’s tail can grow to be almost as long as its body. A newborn rat weighs a few grams, and a mature adult weighs about three hundred grams. Most rats are fully grown by the time they are eight months old. Female rats reach this size in about two weeks and male rats reach full size at around nine months. The average lifespan of a pet rat is about two to three years, but in the wild, rats can live as long as a year and a half.
When it comes to reproduction, rats are polygynandrous, which means they have more than one partner. Their gestation period is around 21 days and they can produce up to five litters each year. Female rats reach sexual maturity around two to four weeks after birth and nurse their young for up to three or four weeks. The female rat can increase its population by up to five times in the course of a year if the conditions are right.
Rats can breed continuously if they have plenty of food available. They will produce litters up to five times a year, with an average litter size of eight to twenty-two rats. The number of litters varies by size, from six when they are young to 11 when they reach 500g.
