How Big Do Guinea Pigs Get: A Helpful Size Guide

Before adopting a guinea pig, you certainly need to learn more about the size of these animals. After all, a lot of things that you buy for them depend on the numbers. This is why we have prepared for you our helpful size guide for guinea pigs.

How long do guinea pigs grow? Guinea pigs are rodents and that’s exactly why a lot of people assume that they are small, but that’s not exactly true. In fact, mature guinea pigs are usually between 8 and 12 inches long (20 and 30 cm). That’s quite a large animal when compared to some other small pets. Of course, the length of the guinea pig’s body depends on a lot of different factors. Whether it’s a female or a male; a baby or an adult. Even the breed can affect the size of the guinea pig. Also, guinea pigs reach maturity and stop growing when they are around 14 months of age. 

Thankfully, unlike the majority of rodents, cavies do not have tails. Sometimes it might be difficult to measure the length of the animal if its tail is as long as the body itself! However, that’s not the issue with guinea pigs.

Now let’s take a closer look at how long your guinea pig should be when it’s born and when does it begin to grow rapidly?


Guinea pig Birth

If you have no intention of breeding guinea pigs, then the chances are high that you might not even see their cute babies. Cavies don’t stay tiny for long as they grow relatively fast. Moreover, pet stores have only the guinea pigs that have already grown a little, so seeing a newborn guinea pig is a truly rare event.

Usually, guinea pig babies are around 3-4 inches long (8-10 cm). Imagine how cute these little fellows are! However, the size of a newborn depends on a variety of factors. Mainly, on the number of pups in the litter. Guinea pigs can give birth to 1-6 cavies at a time. In the majority of cases, three babies are born. Of course, the more pups there are, the smaller they usually are.



Guinea pigs grow until they are around 14 months old. Till this age, they grow very fast! During the first eight weeks, for example, the guinea pig will double in size. So, in about 2 months your guinea pig will be 6-8 inches long (15-20 cm). After the first weeks have passed, the cavy will slow down a bit with the growth, but still reach around 8-10 inches (20-25 cm) in another eight weeks.

By 14 months the guinea pig will reach 8-12 inches (20-30 cm) and that’s when the guinea pig can be considered to be mature. The cavy might continue to grow just a tiny bit, but usually guinea pigs are fully grown once they reach this particular age.

Guinea Pig Helpful Size Guide

Age Size (length)
Birth 3-4 inches (8-10 cm)
8 weeks 6-8 inches (15-20 cm)
16 weeks 8-10 inches (20-25 cm)
14 months 8-12 inches (20-30 cm)


Does the Size of the Guinea Pig Depend on the Breed?

The size of a lot of animals depends on their breed. Dogs, for example, can be huge or, sometimes, as tiny as a guinea pig but when it comes to cavies, does the size of their bodies depend on the breed or not? Well, the truth is that there isn’t a big size variety between guinea pig breeds. In general, practically all of the cavies can grow to around 30 cm (that’s 12 inches). However, there is a guinea pig breed that can grow a little bit bigger!

The Rex guinea pig breed can grow up to…17 inches (43 cm)! Despite the name, the fellow doesn’t look like a dinosaur. It is similar to a Teddy guinea pig, except a bit bigger and with a dense wavy coat. Yes, the Rex guinea pig is a real giant amongst the other breeds. However, that does not mean that if you have your very own Rex it will be exactly 17 inches long.

When it comes to other cavy breeds, the Abyssinian guinea pig, for example, is usually between 8 and 12 inches (20-30 cm). Another popular breed is the American guinea pig. This breed is a little smaller and has a body length between 8 and 9 inches (20-22.86 cm).

Bear in mind that the length of the cavy also depends on genetics, nutrition, the overall health and even on the sex of the animal.

Related: Guinea Pig Breeds: Types, Traits, And Breed Information

How Big Do Male Guinea Pigs Get?

It would seem logical that males have to be a bit bigger than females and that’s exactly the case with guinea pigs.

Male guinea pigs (boars) are not only longer but also heavier than female guinea pigs. In case you have a boy that would mean that the fluffy ball might grow to the breed’s maximum length. American guinea pigs, for example, tend to be between 8 and 9 inches long which means that a male cavy will, most likely, be around 9 inches long.

How Big Do Female Guinea Pigs Get?

In general, female guinea pigs (sows) are smaller than boars. You can even use this information to tell whether the cavy is a male or a female (after the fluffy balls reach the age of 3 weeks).

Sows are not only shorter, but also not as heavy as male guinea pigs. The majority of girls will be between 8 and 10 inches (20- 25 cm) in length.

What Is the Perfect Cage Size?

We have already figured out that guinea pigs are relatively large animals. Especially, taking into consideration that they are rodents. Of course, cavies need enough space to live in and if a small box is enough for a mouse, for example, it won’t do the job for a guinea pig. In fact, if you want to be a great owner to your cavy, you would have to consider buying a large cage from the very beginning as guinea pigs are not only big animals, but also curious and relatively active ones.

Unfortunately, the absolute majority of cages that you can find in the store that are ‘designed’ for guinea pigs are actually too small. Your fluffy ball of happiness has to have a real house with a few ‘rooms’. There has to be a special area where it is going to eat and drink, a toilet and the sleeping area. Moreover, you can also make a ‘playground’. By the way, it will be easier for you to clean a bigger cage with different ‘zones’ as guinea pigs like to keep everything in order.

Usually, the cage has to be more ‘vertical’, if you are a rodent owner. These animals like to climb, dig and so on. However, guinea pig owners should choose cages that have more floor space, as cavies will be spending most of their time running around. You can still have some ramps, but floor space is key.

So, how big should the guinea pig cage be?

The size does not depend on the breed or the sex of your guinea pig. The main thing that you have to take into consideration is the number of guinea pigs in the cage:

  • If you have one guinea pig, then 30”x36” is good cage size.
  • For two cavies get a cage that is around 30”x50”.
  • Have you decided to adopt three cavies? Then pick a cage that is 30”x62”.


It goes without saying that if you used to have one cavy and then decided to get another one, you have to change the cage as well. The cage size is practically as important for the well-being of your guinea pig as nutrition. In small cages, they will get bored, develop all sorts of medical conditions and be dirtier and we certainly don’t want that, right?

Source: Guidelines for the Housing of Guinea Pigs 

Related: What Guinea Pig Cage Size Is The Best? (Proper Accommodation)

Guinea Pig Handling

Guinea Pig Handling

Thanks to the fact that guinea pigs are relatively big animals, it is much easier to hold the fluffy balls. Cavies are great pets for children also because of their size. The kid is less likely to drop the guinea pig because it is not too small. Moreover, it is more difficult to hurt them (but guinea pigs should still be treated with tenderness and respect, of course).

By the way, another great thing about the size of guinea pigs is that they are less likely to crawl into small holes or other places that you won’t be able to reach.


How long do guinea pigs grow? Now you know that these rodents are quite big and that the majority of cavies grow up to 30 cm (12 inches). Their length certainly does depend on a variety of factors but doesn’t drastically differ once the guinea pig reaches a certain age. By the way, remember to make sure that the guinea pig has enough space in its cage as it is extremely important for the cavy’s well-being. Also, we suggest taking a look at the Guinea pig Size-O-Meter to see if your guinea pig is under or overweight. It is very important to determine if your guinea pig has a healthy weight and size. Under or overweight conditions might be a sign of some deeper illness. Best of luck with caring for your guinea pig pet!