What is the Difference Between Rats and Mice?

wiseGEEK Writer

Rats and mice have many differences and similarities. It is challenging to determine specific areas of difference and commonality since there are a number of types of both animals. Usually the two species are compared by evaluating the differences between house mice (Mus musculus) and Norway or black rats (Rattus norvegicus and Rattus rattus). These may also be called pet rats or mice or domesticated versions of each species.

Mice are smaller than rats.
Mice are smaller than rats.

Mice and rats cannot interbreed though they are related. Evolutionary biologists believe the two species share an ancestor, much in the same way that tigers and cheetahs are probably related. Each type of animal evolved differently, selecting certain characteristics that appear to have been of most help in ensuring survival.

Rats make better pets than mice.
Rats make better pets than mice.

Simply from a visual standpoint, you’ll notice immediate difference between Norway or Black rats and house mice. Rats are much larger. At maturity, they weigh about 12.35- 22.93 ounces (350-650 g), and have about a 9-11 inch (22.86-27.94cm) body length. They have long tails, which are an average length of 8 inches (20.32 cm). Their tails are thick and heavy.

A brown rat.
A brown rat.

A mouse, conversely may be one-tenth the weight of a rat, and weighs approximately 1-1.76 ounces (30-50 grams). Mice are shorter, about half the size of rats. They have an average body length of about 3-4 inches (7.62-10.16 cm), and their tails may be slightly more evenly balanced with their bodies, measuring about 3-4 inches. Mouse tails are very thin, and sometimes barely perceptible as compared to the much wider and longer rat tail.

At least in comparison of rats and mice in the species mentioned above, rats’ ears tend to be smaller in proportion to their heads, and they may appear larger, with more blunt features than do their distant relatives. Mice generally have delicate features and have more pointed faces that do rats. From a chromosomal standpoint, differences become even more striking.

Though there is relationship between rats and mice, their separate species are different on microscopic levels. Rats have a higher number of pairs of chromosomes, 22, as compared to the mouse’s 20 pairs. When kept together as house pets, they may create problems for each other. Rats may kill mice and eat mice, most commonly in undomesticated settings, and presence of rats in a home can seriously disturb a mouse. They may breed less or be panicked. If you want both rats and mice as pets, you should consider keeping them in separate rooms.

If you’re considering either animal as a pet, rats tend to be the better choice. They are usually more intelligent and relate better to humans than do mice. There are exceptions, and some wonderful mouse pets exist. In general, though, rats prove to be the better and more easily trained pet.

These differences between rats and mice can change depending upon different species compared. Both have fairly short lifespans in the wild, with about 70% dying before they are a year old. In captivity, lifespans may be similar. Mice might live longer, about five years, but many die at two to three years old. Rats may live about three-four years in captivity. The short lifespans of these animals may not make them ideal pets for young children.

The classic, spring-loaded mouse trap is designed to kill the rodent.
The classic, spring-loaded mouse trap is designed to kill the rodent.

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Discussion Comments


Pet mice do not live five years. The average lifespan of a mouse is 1.5 to 2 years, even when kept in captivity and fed the highest quality foods and given the best of love and care. In 2009, a scientist bred a mouse whose growth hormone receptor was knocked out, leading to this mouse living to an advanced age of five years old. This was part of "Methuselah Project," a study about longevity. A mouse bought from a pet store or breeder will not live this long.


I have had friends with pet rats, and they swore they were some of the best pets ever. While I wouldn't want one, I can see why. They're much cleaner than their stereotypes suggest, and they don't have the same musky smells that other rodents, like ferrets, have even if they're clean. I think they also are not violent if raised in a nice home, though they could certainly defend themselves.


While there are many physical differences between rats and mice, they do have some similarities. Both are more intelligent than you might expect, though rats are smarter. Also, both are good animals for psychological or biological experiments, though mice are usually preferred for this due to their smaller size.


please send me a list of all species of both rats and mice in the world.

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