How Big Do Guinea Pigs Get? | Guinea Pig Size Guide

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

How big do guinea pigs get? Mature guinea pigs are usually between 8 and 12 inches long (20 and 30 cm). When they reach maturity, they stop growing, 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!

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

A Guinea Pig


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 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. 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 they 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). 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

AgeSize (length)
Birth3-4 inches (8-10 cm)
8 weeks6-8 inches (15-20 cm)
16 weeks8-10 inches (20-25 cm)
14 months8-12 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. 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. 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, 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. Cavies need enough space to live in. 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 of your cavy, you would have to consider buying a large cage from the very beginning. 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’. 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. 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.

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” x 50”.
  • For three cavies, pick a cage that is 30”x 62”.

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. We certainly don’t want that.

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

Guinea Pig Handling

Guinea Pig Handling

The fact that guinea pigs are relatively big animals, it 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.

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.


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. 

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.

List of Sources

 Guidelines for the Housing of Guinea Pigs in Scientific Institutions

Guinea Pig Housing

Cavia Porcellus – Guinea Pig