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Description and Physical Characteristics of Rats

By Katherine E. Quesenberry, DVM, MPH, DABVP (Avian),
Kenneth R. Boschert, DVM, DACLAM, Associate Director, Division of Comparative Medicine, Washington University

Adult female and male rats typically weigh 12 to 16 ounces (350 to 450 grams) and 16 to 23 ounces (450 to 650 grams), respectively (see Table: Rats at a Glance). They are about 9 to 11 inches long without the tail. Male rats are usually larger than females. Pet rats are available in several colors and coat patterns due to specialized breeding. The common color variations include brown, black, tan, gray, and white with both lighter and darker shades as well. Some of the more exotic colors are Siamese, blue, silver black, silver fawn, lilac, cinnamon, black-eyed white, cinnamon pearl, lynx, silver agouti, silver lilac, and blaze. Rex rats have a curly coat. Tailless rats are born with no tails and hairless rats have no fur. The average life span of rats is about 2.5 to 3.5 years.

Rats at a Glance


2.5 to 3.5 years


Body: 9 to 11 inches (23 to 28 centimeters)

Tail: 7 to 9 inches (18 to 23 centimeters)


12 to 23 ounces (350 to 650 grams)

Cage temperature range

64 to 78°F (18 to 26°C)

Relative humidity

40 to 70%

Breeding age

4 to 5 weeks

Estrous cycle

4 to 5 days

Gestation period

21 to 23 days

Litter size

6 to 12 young

Weaning age

21 days

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