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When Do Guinea Pigs Stop Growing and How Big Do They Get?

Tim Rhodes
Written by Tim Rhodes Last Updated: November 17, 2022

Guinea pigs are a popular pet for many reasons – they’re relatively low-maintenance, gentle, and have a plus personality.

But one question potential owners often have is: how big do guinea pigs get? And when does a guinea pig stop growing?

In this article, we’ll answer both of those questions so that you can be prepared for your new furry friend.

When do guinea pigs stop growing?

Guinea pigs usually reach full size by around six to seven months old. However, some may continue to grow and fill out for another month or two after that.

Once your guinea pig reaches full size, he’ll still continue to mature and develop. For example, his coat will continue to fill out and become more lustrous.

guinea pig teeth

He may also develop more personality as he gets older and becomes more used to his surroundings.

So even though he’s not getting any bigger, there’s still plenty of room for him to grow and change in other ways.

How big do guinea pigs get?

Most adult guinea pigs stay between 20 and 30cm long, with anywhere between 450 and 700g being a healthy weight.

Some breeds can grow slightly larger, while others stay smaller. You can expect your guinea pig to reach its full size by around 8 months old. 

Once fully grown, your guinea pig’s length will depend on the breed. The smaller breeds such as the dwarf cavy, this means they’ll only get to around 20-25cm.

female guinea pig

On the other hand, the larger guinea pig breeds can grow up to 35cm, such as the American blue cavy.

The most common type of guinea pig, however, is the English short-haired cavy which sits somewhere in the middle at around 30cm once fully grown. 

The American Guinea pig, another popular breed, is slightly larger than the English short-haired cavy at around 32cm.

When it comes to weight, they will fall between 450g and 700g when mature. Anything outside of this range is considered unhealthy and you should take your pet to the vet for a checkup.

guinea pig owners

Female guinea pigs tend to be on the lower end of this spectrum, while male guinea pigs are generally at the higher end.

For example, male guinea pigs may weigh up to 800g while female guinea pigs will rarely exceed 600g.

Regardless of gender, though, a sudden jump or drop in weight can be a sign of an underlying health condition and is something you should always keep an eye on. 

How big can baby guinea pigs get?

Baby guinea pigs, also known as pups, are usually about 8-10cm long. Pups grow quickly and can reach their full adult size of 30-35cm within 6-8 weeks.

Some may continue to grow until they are 12 weeks old. Some may even reach the size of an adult guinea pig within just a few weeks.

American Cavy Breeders Association

However, it is important to note that not all pigs will grow at the same rate. Some may reach their full size sooner while others may take longer.

So, if your baby guinea pig seems to be growing slowly, don’t worry – he’ll probably catch up eventually.

What is the growth rate of guinea pigs?

Healthy Weight

Guinea pigs grow quickly, especially in the first few weeks of life. Pups can gain up to 10g per day and may even double their weight within a week.

After the first few weeks, though, the growth rate slows down considerably.

By the time they are 8 weeks old, most guinea pigs will only be gaining around 5-10g per week.

What factors affect the size of a guinea pig?

There are a few things that can affect a guinea pig’s size. One is the breed. Some breeds are just naturally larger than others.

Another factor is whether you have a male or female. Females are usually smaller than males.

pet store

If you have two guinea pigs, they might also be smaller because they have to share food and space.

The last thing that can affect the size of guinea pigs is their diet. A healthy diet of hay, vegetables, and guinea pig pellets will help your guinea pig reach its full potential size.

So, there are a few things to keep in mind when it comes to guinea pig size. But don’t worry, with a little care and attention, your guinea pig will be just the right size for you.

Guinea pig growth chart by age

In case you’re wondering how big your pet will be at different stages in its life, we’ve put together a handy average guinea pig weight and growth chart.

Please note that this chart is a general guide only, as the size of a guinea pig can vary depending on the breed and other factors.

2 months of age:

Length: 10-15 cm; Weight: 80-120 g

4 months of age:

Length: 15-20 cm; Weight: 200-250 g

6 months of age:

Length: 20-25 cm; Weight: 350-450 g

8 months of age:

Length: 25-30 cm; Weight: 450-700 g

12 months of age:

Length: 30-35 cm; Weight: 500-650 g

As you can see, they grow quickly, especially in the first few months of life. After that, they will continue to grow slowly until they reach their full adult size.

How do I ensure my guinea pigs reach their full-size potential?

The first step is to choose the right breed. Some breeds grow to be larger than others.

If you’re looking for a big guinea pig, choose a breed like the Texel or the British Giant.

The next step is to feed your guinea pig a high-quality diet. A diet rich in hay, fresh vegetables, and pellets will help your guinea pig reach its full potential.

Avoid feeding your guinea pig too many sugary treats, as this can lead to obesity and health problems.

rex guinea pig

Finally, provide your guinea pig with plenty of space to exercise. A large cage or enclosure will give your guinea pig room to run and play.

They also love to play with toys, so consider adding some tunnels, balls, and other toys to their home.

By following these tips, you can help your guinea pig reach its full-size potential.

Frequently asked questions (FAQs)

There are a few things to keep in mind when it comes to guinea pig size. Here are some frequently asked questions that will help you understand more about guinea pig size.

Do guinea pigs stop growing?

A guinea pig reaches its full adult size by around six months old. After that, their growth rate starts to slow down and they will only put on a small amount of weight each year.

How much should a guinea pig weigh?

Most full-grown guinea pigs weigh between two and four pounds. Of course, this depends on the breed and the diet of the guinea pig.

What is the average lifespan of a guinea pig?

The average lifespan of a guinea pig is four to eight years. However, some have been known to live for 10 years or more.

How long do guinea pigs stay young?

Guinea pigs reach maturity at around six months old. After that, they start to age slowly and can live for four to eight years. However, some have been known to live for 10 years or more.

What is the biggest guinea pig on record?

The biggest guinea pig on record was a British Giant named George. He weighed 7 pounds 8 ounces and was 29 inches long.

Do bigger guinea pigs live longer?

Some studies have shown that larger guinea pigs tend to live longer, while other studies have found no correlation between size and lifespan.

Do bigger guinea pigs need more food?

Bigger guinea pigs do not need more food than smaller ones. In fact, they actually eat less per pound than smaller guinea pigs.

These are some things to keep in mind when it comes to guinea pig size. As you can see, there is a lot of variation in size, depending on the breed and other factors.

If you have any further questions, please consult your veterinarian.

Final thoughts

Guinea pigs come in a variety of sizes, depending on the breed and other factors.

They usually reach their full adult size by around six months old. After that, their growth rate starts to slow down.

It is important to choose the right breed and provide a high-quality diet if you want your guinea pig to reach its full-size potential.

Additionally, they need plenty of exercise, so be sure that your guinea pig’s cage or enclosure is large enough for them to run and play.



Tim Rhodes
Tim Rhodes

Hi there! My name is Tim Rhodes and I'm a guinea pig enthusiast through thick and thin. My mission is to teach others useful tips and tricks about these cute creatures. When I'm not writing, I enjoy kickboxing and work as an animal trainer.

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