Mice Aren't Baby Rats - 20 Differences Between Rats And Mice

Mice Aren't Baby Rats - 20 Differences Between Rats and Mice

For my fellow rat enthusiasts, the difference between pet rats and mice may seem very obvious. But for our friends and family, I’ve seen them commonly intermixed in conversation. While this is a rat page, I love all rodents, and encourage people to learn about them!

While both in the Muridae family, and in possession of a similar body structure at first glance, pet rats and mice are vastly different. Though it’s sometimes mistakenly thought rats are just large mice, their physiology, behavior, and needs are all unique to their own species.  

While it may not seem important to know the differences between these two species, if you ever plan on owning either pet rats or mice, it’s important information to know! That’s why I’ve compiled an easy list of differences to help you in your journey of learning about rats, or simply to share with your friends the next time they refer to a mouse as a “baby rat”.

Are There Any Similarities Between Pet Rats and Mice?

For the purposes of this article, both the rats and mice referred to are of the fancy variety commonly kept as pets. The term “rat” actually covers a wide number of rodents, all sharing their own differences to each other. Needless to say, if we tried to include them all, we would be here all day!

While rats and mice do share some similarities, the number is very small compared to their differences, and doesn’t constitute an entire list. The biggest similarity is their scientific family they share – Muridae. This family contains over 700 species, so is almost more an argument for their difference!

A big similarity is they are both crepuscular animals, as is common in rodents. This means they aren’t entirely nocturnal, but are most active at night. They also can both eat the same type of food in general, so if you own both rats and mice, you can buy block food in bulk and add certain other foods to fit their unique needs!

Lastly, they are both incredibly cute pets, and while I don’t currently own mice, after researching them I think I might have to get some in the future!

20 Differences Between Pet Rats and Mice

Physical

The physical differences between rats and mice are the easiest to spot. They’re right in front of us and we don’t have to spend a lot of time with the critters to notice! You can even notice these differences on wild mice and rats.

1. EARS – While both rats and mice have adorable ears, they’re one of the defining features that separates them! You’ll notice rat ears are smaller in relation to the head than mouse ears. This is especially noticeable on top eared rats.

2. TAILS – Unlike rodents like gerbils, rats and mice both have (mostly) naked tails. But if you look at the animals as a whole, you’ll see mice have tails that are longer and thinner in proportion to their body than rats do!

3. FEET – If you own rats, you know how their front feet look all cute and adorable, especially when they go and do something like grab your finger and attempt to bring you into the cage with them. Then you look at your back feet and they look like dragon talons!

Not so with mice. They have tiny little feet all around, adding to their dainty appearance. Even their front feet are smaller than rats relative to their body size.

4. NOSE – Both rats and mice have the same type of nose, but mice noses (as with most things as you can see) are smaller. Mice noses also come to a point, whereas rats’ noses are more broad, giving a blunter appearance.

5. HEAD – The differences of the noses in rats and mice also contribute towards a difference in the appearance of their heads. Mice have an almost triangular appearance to their heads, while rats’ heads appear much “boxier” or square-shaped, especially the males.

You can also see a difference when comparing the size of the heads of rats and mice to their bodies. Mice have a small dainty head in proportion to their bodies, while rats have a head that can sometimes seem quite large for their bodies.

Fun Fact: A rat can fit through anything they can fit their head through.

Keep this in mind when buying a cage or choosing a place for them to free roam!

6.    BODY SIZE – At this point, it goes without saying that rats are much larger than mice! Even a young rat will be bigger than an adult mouse.

The average weight of an adult mouse is 30 g. Baby rats can sometimes hit this benchmark at just three weeks old! At four weeks old, the average rat has almost tripled this weight at 88 g!

The average length of an adult mouse is merely 6 inches! Especially taking into consideration the tail is as least as long as their body, that’s not a very long body! Rats, on the other hand, measure an average of 18 inches.

For reference, a 4 week old baby rat may be the same length as an adult mouse (but much heavier!).

7. NIPPLES – Yes, you read that right! Rats actually have 6 pairs of nipples as opposed to mice, who only have 5 pairs of nipples. While this may be hard to check on such squirmy animals (and impossible on males who do not have nipples), I still thought it was a super neat difference to share!

8. FECES – This difference is more helpful if trying to figure out if you have mice or rat “guests” in your home, but it’s easy to tell if you find their excrement. Rat feces is significantly larger than mouse feces, but interestingly enough, mice poop more than rats throughout the day!

Physiology

Physiological differences, though not as extensive as the physical differences, are an interesting distinction between rats and mice. Though they look similar to a lot of people, there are key differences in the genetics and build of rats and mice.

9. GENETICS - You might think rats and mice have similar genetics, but rats actually have 21 chromosome pairs, as opposed to mice, who have 20 chromosome pairs. 

While this may not seem like that big of a difference, there are certain genes found in rats that are not found in mice. In a publication by the National Human Genome Research, they found “genes involved in immunity, the production of pheromones (chemicals involved in sexual attraction), the breakdown of proteins and the detection and detoxification of chemicals.” that were not found in mice.

10. LIFESPAN – The sad reality is, the lifespan of rats is far too short. We get attached and make this great relationship with our little furry friends, and they leave us with a rat-shaped hole in our heart an average of 2 years later.

But as short as rats’ lifespans are, mice lifespans on average are shorter. The average fancy mouse has a lifespan of 1-2 years, whereas the average fancy rat has a lifespan of 2-3 years. 

While there are variables, when keeping rats and mice as pets expect a shorter lifespan from our smaller friends.

11. BREEDING – Like rats, mice can have a litter and then get pregnant again just 3 days after giving birth. However, the gestation period is understandably shorter for mice than for rats. 

Because of this, mice can have more litters per year than rats. Though this is just a fact, not something that should be followed, as back to back breeding is irresponsible for both rats and mice.

In my research, there was wide variation on average litter sizes of mice, but it is possible for them to have 20 babies! Rat litters tend to be in the 6-12 range, but litters can vary from just 1 to 22 babies. 

Now the big question - is it possible for a mouse rat hybrid exist? As cool as that sounds, the answer to this is no. First of all, because they are natural enemies and won’t be attracted to each other to mate. 

Even if artificial insemination is attempted, mice and rats eggs have a defensive layer protecting other species’ sperm from entering the egg. Even if it was possible, the moral question would have to be raised of whether it would be ethical.

From the differences seen above, it’s theoretically entirely possible the offspring could be rejected by both mice and rats, or show aggression towards other mice.

Behavior

Rats and mice are both prey animals, and will thus act in a manner befitting their spot in the “circle of life.” They often require patience and a lot of love to grow comfortable with their humans. However, there are key differences between rats and mice in their behavior.

12. BASICS - Mice are naturally curious, where rats are naturally cautious. If you've ever tried to give a new treat to a stereotypical new rat you haven't earned the trust of you know what I'm talking about! For months, one of our rats was so careful about what she ate she wouldn't accept anything given to her outside her cage.

While I’ve never personally owned mice, I can see their curious behavior at the pet stores (though I don’t recommend buying any animals from there). When I walk by their tanks, all of them seem so curious about the large creature walking by!

The cautiousness of rats should not be mistaken for them not wanting attention from their humans. One of my most attention seeking rats is also one of my most cautious, preferring my lap to free roaming, and startling at every noise or change. 

13. SOCIALIZATION - Both rats and mice benefit greatly from socialization with their own kind (with the exception of male mice). But their socialization with humans is a bit different.

While there are rats who are more standoffish and mice who are more in your pocket, rats tend to be more interested in their human friends than mice are. 

Imagine rats like little dogs and mice like little cats. Like dogs, rats benefit greatly from interaction with their owners. My rats pine at the front of their cage for me whenever I walk by, and when I let them out they just want to climb all over me!

Mice can be affectionate to their owners, it just (usually) takes a little longer to get there, and they don’t require as much time with their owners as rats do.

It is ESSENTIAL rats and female mice have same species companions!

If you’re looking for rodent-type animals you can really bond with, there really isn’t anything better than rats!

14. TRAINING - Mice can be trained to do tricks, but rats are much easier to train due to their eagerness to please. 

For example, one of my rats, Buttons, picks up tricks almost instantly, often mastering them in the first session. Even after weeks of not doing the trick, she remembers the signal and will perform even a trick she just briefly learned. 

This especially extends to litter training. Rats generally grasp the concept relatively quickly, but it’s harder to litter train mice. This is because, while rats do mark, mice do so almost constantly.

15. MALES - I’m no expert in mouse-keeping, so in my research, I’ve found differing opinions on the matter of housing male rats together. Some people say male rats must live alone, others say they need a lot of space if they’re housed together to negate territorial fights.

However, male rats have no problem being housed together (if introduced properly), and actually love to snuggle with their cage mates! 

If there are problems with aggression and territorialism, it’s a viable option to neuter male rats, whereas the risks outweigh the benefits of neutering male mice. 

Care

We all love our pets, and want to take great care of them. That’s why it’s important to understand that even though rats and mice are rodents, they require different levels and types of care. If you’ve owned rats before and want to get mice (or vice-versa), knowing the differences in levels and types of care is vital!

16. HANDLING - Because mice are so much smaller and fragile than rats, more care should be taken when handling them. One of my rats loves to divebomb off my shoulder, which scared me at first before realizing how durable rats can be!

As you read in the section on the size differences between rats and mice, mice are way smaller than their rat cousins. Because of this, rats make much better pets for children who don’t quite understand their strength yet than mice do. 

Note: Care should still be taken when introducing pet rats to your young children. Teach them the proper way to handle them, and take into consideration whether your child is old enough to understand how to properly hold the rats without squeezing them too hard.

17. FEEDING – The basic feed requirements for rats and mice are actually quite similar. However, rats need a higher level of fiber and a lower level of fat than mice do.

If you’re feeding both your rats and your mice the same pellet food, be sure to supplement where needed to meet their daily nutritional requirements.

18. ENVIRONMENT - Unlike rats, I’ve read mice can live in an aquarium, provided it is large enough and kept very clean. However, it's best for their lungs to keep them in a bar cage, though it is important to buy a cage with small gaps so you don’t find yourself with a bunch of loose mice and nowhere to keep them secure!

Reminder: NEVER keep rats in an aquarium!

Because of their smaller size, mice don’t need as big a cage as rats, though like rats, I’m sure they appreciate larger areas to run and play! 

Mice are also easier to buy cage accessories for. Like rats, if they have a wheel in their cage it needs to be big enough so they don’t need to bend their spine to run. But because they’re so much smaller, mouse-safe wheels are cheaper and easier to find than rat-safe wheels.

Finally, if you have both rats and mice, it is best to keep them in separate parts of the house. Just like rats can be frightened by the smell of a cat or some other predator, mice can become very stressed at having to smell or see rats.

19. TIME REQUIRED – As I stated before, rats are a bit more like dogs than mice, in that they need more interactive time out of their cage than mice do. Rats are a lot larger than mice, and do best with at least an hour of “free roam” time every day, and the more the better!

Unless you have a dedicated contained space where the rats can run around unsupervised, this means you need to be able dedicate a significant amount of time each day to their exercise, much like walking a dog. 

Rats also crave attention from their human owners much more than mice do. I swear every time I walk by my rats’ cage and don’t take them out, they all crowd to the front and give me the saddest eyes!

Mice, while they still benefit from attention, are more like cats than dogs. As long as they have companions, they don’t need nearly as much personal attention as rats do. The exception is the lone male mouse, as you are the only companion he will have, and so will need more attention than your female mice.

20. KEEPING RATS AND MICE - Read this, and then read it again, cause it’s probably the most important difference between mice and rats.

Rats and mice CANNOT cohabitate!

They are natural enemies, and will fight each other to the death. Keeping both animals is fine, as long as they are kept humanely and ALWAYS kept separate from each other.

Why Understanding Their Differences Matters

So why does all this matter? Besides knowing for knowledge’s sake, potential owners and current owners of rats and mice can benefit greatly in knowing differences for the animals’ best interests. This is especially true as we see it’s common for all rodents to be lumped together in products at major pet stores and brands.

Understanding the size and fragility of mice might mean you realize they don’t make the best pets for younger children. Realizing you don’t have a ton of time to dedicate to an animal might mean you get a few female mice instead of rats. 

Or you may not have known that rats and mice cannot cohabitate (I didn’t before owning rats)! To illustrate why this is such a vital difference to understand, you have to understand that though both rats and mice are territorial, rats are significantly bigger, and will almost always win in a fight.

I’ve even heard of some people using their rats as mousers, since many times rats will “clean up after themselves” but would not recommend this, as pet rats can contract diseases from wild mice. 

That being said, since it’s in their nature to kill mice, never put rats and mice together, even for a cute picture or to let them “play”.

Final Thoughts

Whether you own pet rats or mice, we can all agree that they make great pets, and don’t get nearly the credit they deserve! Hopefully understanding the differences between these two pets will help you whether you just didn’t know about the differences or are trying to decide which pet is best for you. Interested in also knowing the difference between male and female rats? We cover that here!