How Big Do Guinea Pigs Get?

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big caricature guinea pig

The guinea pig is a popular household pet in western societies due to its ease of care, affectionate disposition, and small size. 

It doesn’t take up much space in the house and is relatively inexpensive to purchase and care for. It also won’t eat a lot given its size and at least you don’t need to worry about breaking your bank account by spending a lot on food.

Other rodents such as hamsters and mice are too tiny to cuddle and dogs are too big. Guinea pigs are just the right size. And even though they might be small, they certainly have big hearts. Size truly doesn’t matter when it comes to the guinea pig.

But are they really that small? How large are fully grown guinea pigs? Let’s find out.

Factors That Influence Size Of Guinea Pigs

Just like with other animals and even humans, a guinea pig’s size can vary depending on gender, lifestyle, diet, age, how many siblings it has, and genetics.

Males, called ‘boars’, tend to grow a little larger than females, called ‘sows’.

A guinea pig that lacks exercise and has an unbalanced diet may show signs of stunted growth and may turn out to be under or overweight. In order to grow to the expected natural size, a cavy needs supplemental fruits and vegetables in its diet. To keep the immune system working strong, Vitamin C must be provided either in the form of either fruits or commercially-available drops.

Keep in mind that there are plenty of foods that are dangerous for guinea pigs. Examples include legumes, cabbage, potatoes, avocados, and anything from the onion/garlic family.

Any plants that have bulbs are toxic to guinea pigs. To keep a cavy healthy, strong and at its optimal size, good foods to include in its diet are cucumbers, carrots, and rutabaga.

Baby guinea pigs called ‘pups’ naturally begin life at a small size and gradually get bigger as they progress into adulthood. Pups can differ in size depending on their birth order.

A litter with more pups may contain smaller-sized guinea pigs than a litter with fewer pups. This, of course, happens because the more pups there are, the less space there is inside a sow’s ovaries. The size of an average cavy litter is three, but a sow can give birth to as many as six.

Studies have shown that genetics can also play a role in increasing or decreasing the size of any given guinea pig.


Guinea Pig Dimensions

Compared to other rodent pets, the guinea pig perhaps grows the largest.

Newborn pups are only about 3 – 4 inches long and weigh somewhere between 0.13 and 0.26 pounds. They grow very fast and will double in size and weight by the end of their 8th week.

After 2 more months, they’ll double in size and weight again and then continue to grow until they reach maturity; after which time they will have reached adult size and cease to grow any further.

The average weight of an adult or fully grown boar falls between 2 and 3 pounds. An adult sow’s weight is a little less, around 2.5 – 3 pounds.

As previously mentioned, since there are various factors that can influence their size, the average weight of either male or female guinea pigs will usually be somewhere between 1.5 and 2.6 pounds. A measurement ruler can be used to capture a guinea pig’s dimensions accurately.

Cavies don’t have much of a tail to speak of, so when measuring their dimensions, the tail isn’t counted. From the back of the rump to the tip of the nose, an adult’s length usually ranges from 8 to 12 inches.

A popular theory currently circulating on the internet is that a guinea pig’s size varies depending on the breed. Unfortunately, there isn’t currently any scientific evidence to support this theory. Guinea pig breeds mostly conform to the average guinea pig size, with no specific breed having a significantly larger or smaller size advantage.

Carlye Yancey
Carlye Yancey


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