According to experts, domesticated rats may reach up to 12 inches in length and up to 5 inches in width. However, due to a shorter life expectancy, those found in the wild typically do not live long enough to exceed 10 inches in length and 3 inches in width.
Since they are well fed, pet rats often appear pudgier with visible rolls and contours. The bodies of most wild rats tend to be more streamlined, as rats living in the wild get more exercise while hunting for food and food may be scarce. While wild rats may visibly appear to be bigger, this is typically due to their tendency to puff their fur in response to the perceived threat of humans.