Most common rats are about the size of a small adult’s hand for the body, and roughly the length of a forearm when you include the tail.

Typical wild rats

  • The common brown (Norway) rat’s body is usually about 6–10 inches (15–25 cm) long, with a tail of about 4–9 inches (11–24 cm).
  • Altogether, that puts many adult brown rats around 10–18 inches (25–45 cm) from nose to tail tip and weighing roughly 7–18 ounces (200–500 g).

Pet (fancy) rats

  • Pet “fancy” rats generally reach about 9–11 inches (23–28 cm) in body length, with the tail bringing them to about 16–20 inches (40–50 cm) total.
  • Healthy adults often weigh around 0.7–1.4 pounds (300–650 g), with males tending to be a bit larger and heavier than females.

Biggest rat species

  • Some of the largest wild rat species can be much bigger than city rats, reaching close to 30 inches (around 75 cm) from nose to tail and several pounds in weight.
  • These giants are rare and usually live in remote regions; the rats seen in homes or cities almost always fall well below these extreme sizes.

How small rats can be

  • Smaller species like roof (black) rats typically have bodies about 5–8 inches (13–20 cm) long, with tails that can be as long or longer, for a total length up to around 16 inches (40 cm).
  • Young rats can be very tiny—juveniles may be only a few inches long in the body before they grow into the adult ranges described above.

Information gathered from public forums or data available on the internet and portrayed here.