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How Big Do Guinea Pigs Get? (Size + Growth Chart)

Kristin Hitchcock

Guinea pigs are smaller animals, though they are actually quite large for a rodent. When you first adopt a guinea pig, you may be getting and adult or a juvenile. If you adopt a smaller guinea pig, it is important to ensure they are growing along the right timeline. Otherwise, it could signal that something is wrong.

In this article, we’ll look at how big a guinea pig should be as every stage, as well as some information you may need when measuring your rodent.

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Fact About Guinea Pigs

Guinea pigs are native to the Andes of South America, which is why they often have longer hair than other rodents. They’re used to a colder climate. The origin of the name “Guinea Pig” is actually very unclear, especially considering that these animals aren’t related to pigs and aren’t from Guinea.

These animals are now fully domesticated, which wild guinea pigs not existing naturally in the wild. Instead, they are likely descended from a different species and evolved next to humans over thousands of years – like dogs.

In the Western world, they are often kept as pets. They were first introduced in the 16th century and have been kept as pets ever since. Their docile nature made them instant hits. Many specialized breeds have developed since then.

In the Andean people, the guinea pig is often raised as a food source. They are also important parts in folk practices, hinting at how long ago they were domesticated.

guinea pigs
Image Credit: Jaroslaw Slodkiewicz, Unsplash

Guinea Pig Size and Growth Chart

The information from this chart shows the standard growth of a Hartley Guinea Pig. Males will be bigger than females.

Age Weight Range (grams)
2 weeks 250 – 150
4 weeks 400 – 285
6 weeks 550 – 350
8 weeks 700 – 400
10 weeks 800 – 500
12 weeks 900 – 550
14 weeks 950 – 600

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When Does a Guinea Pig Stop Growing?

Usually, guinea pigs are considered adults at 6 months of age. This is around 24 weeks. However, growth will slow substantially at about 14 weeks. At that point, they will not actually get much bigger. Males are almost always bigger than females, usually, be a few hundred grams. However, all guinea pigs stop growing at the same time, no matter their gender.

You can judge a guinea pig’s full size quite accurately at 14-16 weeks, though they may gain a few grams afterward. Usually, after 14 weeks, they are simply packing on fat – not actually getting much bigger.

guinea pig on grass
Image Credit: minka2507, Pixabay

Factors Affecting the Size of Guinea Pigs

The most obvious factor is gender. Males tend to be quite a bit bigger than females, no matter the breed. You can expect all males to grow at a faster rate, though both genders will stop growing at about the same time.

Another factor is the breed. Some breeds are bigger than others. The Hartley guinea pig is one of the most common, especially in the scientific community. Therefore, we have the most scientific information about their growth rate. However, other breeds will grow at different rates and reach different sizes.

Diet can also affect the size. However, if fed correctly, all guinea pigs should keep up with others of their gender and species.

Ideal Diet for Maintaining a Healthy Weight

Guinea pigs need a variety of foods to thrive. Typically, they need unlimited amounts of hay. This hay should be low in calcium, such as Timothy hay. They will need to be supplemented with pellets, which will contain more nutrients and help the rodent stay healthy.

Guinea pigs can also eat a variety of fruits and veggies, though you should be careful in choosing the correct options for your guinea pig. Treats should be fed sparingly if at all, as guinea pigs are very small.

guinea pig eating hays
Image Credit: Alexas_Fotos, Pixabay

How to Measure Your Guinea Pig

When judging the growth of your guinea pig, you should focus mostly on the weight – especially if you have a younger animal. While you don’t want your guinea pig being overly large for their length, comparing their length to their weight is not always an accurate way to judge whether a guinea pig is at a healthy weight or not.

Measuring a guinea pig can be a bit difficult. The animal will likely not stay still for an extended amount of time, which can make measuring difficult.

The easiest thing to do is use a kitchen scale, distracting your guinea pig with a treat or affection. Put a paper towel in the bottom of the scale to give your guinea pig some extra grip, which may help them feel a bit safer.

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Conclusion

Guinea pigs all grow at about the same rate, though it can vary based on the breed. In general, males will grow faster than females and end up a few hundred grams larger. In most breeds, females and males are rarely the same size.

While diet can affect the growth rate, all guinea pigs given the appropriate diet should grow at the correct rate. Most guinea pigs will keep growing for at least 14 months. However, their growth slows down substantially at 14 weeks, which you can generally guess their adult size. They won’t get much bigger after that.


Featured Image: Tettania, Shutterstock

Kristin Hitchcock

Kristin is passionate about helping pet parents create a fulfilling life with their pets by informing them on the latest scientific research and helping them choose the best products for their pets. She currently resides in Tennessee with four dogs, three cats, two fish, and a lizard, though she has dreams of owning chickens one-day!