When Are Guinea Pigs Full Grown? 4 Life Stages!

When are guinea pigs full grown? Most people think that baby guinea pigs do not grow up and will just remain a hamster’s size. But this is not the case.

Here’s a fact:

when are guinea pigs full grown

Guinea pigs grow at a fast rate, just like any other kind of small rodents.

More so, guinea pigs mature rapidly, so you should keep the guinea pigs separated until you are already a hundred percent sure about their genders. That is because they can also start mating at an early age.

Going back to the question of when doing guinea pigs grow fully grown, there would be no fixed answer to this.

But they generally become adults after six or eight months. I know it would be hard to know their age, especially when you adopted a wild cavy. (please read here how big do Guinea pig grow)

Here’s the thing:

You can use their weight in finding out!


Life Stages Of Guinea Pigs 

It is important to know the life stages of guinea pigs and the proper way of taking care of them at different stages.

Through this, you can ensure to give them the things that they need to fully develop.

So, when are guinea pigs full grown?


Stage #1. Newborn guinea pigs

For the most part, guinea pigs are already mature when they are born. They can even start eating solid food after a few hours, unlike most animals that take several days.

Much more, newborn guinea pigs can survive, even without nursing. However, there is a possibility that their growth will be affected.

When are guinea pigs full grown

But typically, mother guinea pigs will nurse her babies until they are three weeks old.

Sometimes, in just two weeks, she will stop nursing them because guinea pigs mature real fast, as I have said earlier.

At that point, she will undergo another cycle of her estrus. This stage is also when she will start losing interest in the young ones.


Stage #2. Young guinea pigs 

From birth up to six months old, guinea pigs are considered young.

And as mentioned earlier, young guinea pigs grow fast, just like any other developing animals.

Take note that at this stage, they need more nutrients and calories as compared to adult ones.

So to meet their needs, the diet of young guinea pigs should be nutritionally complete.

Alfalfa-based and fortified food is recommended to be served to them.

Experts would also suggest mixing the alfalfa hay with other grass hay like orchard or western timothy.

Doing so will ensure that they will be getting sufficient amounts of nutrients that they need, particularly fiber.

Much more, proper environmental development in a space that is pet-proofed is also necessary.

A large space is recommended as this will allow them to safely explore, play, and run around. (please read here how much space do Guinea pig need)


Stage #3. Maturing guinea pigs

When your guinea pigs reach 16 weeks of age, it is the time that they mature significantly.

Commonly, their size would be ranging from eight to ten inches.

Life Stages Of Guinea Pigs 

At this stage, you have to feed your developing guinea pigs with pellets specially formulated for them. Preferably, you have to do this two times a day.

An unlimited supply of grass or hay should also be made available to ensure that they develop properly.

For female guinea pigs, you need to add more vitamin C to their diet to keep them healthy. You can do this by adding drops of vitamin C into their water every day.


Stage #4. Adult guinea pigs

In general, guinea pigs are considered adults when they are about six months old up to five years old.

Although adult guinea pigs do not grow anymore, they still need macro-nutrients, including protein and fiber.

Other than that, they also need micro-nutrients, including the variety of minerals and vitamins that are commonly present in a timothy-based uniform fortified food.

Ensure that your pet always has a variety of timothy hay as well as other grass hay. The more variations are available to them, the better.

Remember, alfalfa should only be given to them as an occasional treat.

Most of the adult cavies should also be stimulated to exercise to not gain much weight. As such, you have to ensure that you allot time to interact with your companion daily and have them moving even just a little.

The environmental enrichment, along with constant interaction, can contribute to your pet’s overall quality of life.


Sexual Maturity Of Guinea Pigs

Guinea pigs generally sexually mature when they reach between three and four months old.

Even though they can breed at this age, it would be best to wait until they are about five or even six months old before you allow them to mate.

Sexual Maturity Of Guinea Pigs

Your vet can easily neuter a male guinea pig. However, with female ones, abdominal surgery is a bit more complicated.

Again, guinea pigs reach sexual maturity at an early age, so if your cavy is weaned, there will be a higher possibility of pregnancy and breeding.


Size Of Guinea Pigs

Newborn guinea pigs normally weigh around 1.5 up to 4 ounces. The average weight is ranging between 2.5 and 3.5 ounces.

But this varies depending on how large the litter is. A litter with more offspring tends to have a smaller average weight.

When full-grown, female guinea pigs can weigh somewhere between 1.5 and 2 ounces.

On the other hand, male rabbits can weigh between 2 and 2.6 pounds.


Caring Guinea Pigs 

Guinea pigs are expected to live up to four or even eight years. Five years of life span would be the average. (please read here how old do Guinea pig live)

But proper care can help them live longer than usual.

As such, you have to make sure that your guinea pigs always have sufficient amounts of timothy hay and grass available to them.

That’s why I always make sure that my pet, Ginger, has a sufficient amount of this food. Sometimes, I give him fruits and vegetables that are good for him.

caring guinea pigs

Also, remember that fiber gives them the energy for the day, but it also helps them in wearing down their teeth that are growing continually.

More importantly, they should also have constant access to clean and fresh water. You can also give them a small portion of fruits and vegetables as they contain vitamins and minerals.



When are guinea pigs full grown? You will know that your pet has finished growing through its weight.

A guinea pig starts reaching and filling out its weight when it reaches six or eight months old.

Take note that adult guinea pigs normally weigh from three pounds or even beyond this.

When they are at the age of six months, they are way larger than other rodents such as mice and hamsters. So they might not fit in the enclosures that are designed for those rodents.

If you acquire a guinea pig when it is still a baby, make sure to take into account its potential size when it finally grows into an adult.

You will notice after a few months that they are bigger than you think they would be.

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