How Big Do Guinea Pigs Get?

If you want to know how big your guinea pig will get, you’ve come to the right place.

 In this guide, we will discuss the size of a baby and adult guinea pig, when a guinea pig is considered as fully grown, and also the breed-wise size differences.

Knowing this information will help you assess if your guinea pig is getting the right nourishment and is healthy and thriving.

Let’s get straight to it.

How Big Do Guinea Pigs Get?

Most adult guinea pigs reach a length of 20 to 50 cm which is 8 to 20 inches. The average, domesticated or captive guinea pig grows to 10-12 inches in length and measures about 5 inches in height. Most weigh between 30 and 40 ounces.

Wild guinea pigs are almost as big as the captive ones. They grow to a size of 8 inches in length and around 4-5 inches tall.

Physiologically, there isn’t much difference between wild and captive pigs. We must keep in mind the fact that wild guinea pigs have greater stress in terms of searching for food and staying away from predators.

These factors can play a role in their growth.

For example, some wild giant guinea pig breeds like the Rex are nearly one and a half times bigger than the average domesticated breed sizes.

Rex cavies reach a length of around 17 inches and weigh between 25 and 45 ounces. You also have captive or domesticated Rex cavies.

In all, there are 13 different known breeds of guinea pigs that are kept as pets. They are more or less of the same height and weight. We will discuss the breed-wise sizes shortly.

How Big Are Baby Guinea Pigs?

At birth, a guinea pig weighs around 100 grams or about 3.5 ounces and measures 8 to 10 cm or 3-4 inches in length. By the time they are 2 weeks old, they measure around 5 inches long and weigh around 200 g or 7 ounces.

At 4 weeks, your young guinea pig weighs around 400g or 14 ounces and measures between 6 to 7 inches long. By 8 weeks, most guinea pigs weigh between 500 and 700 grams or 17-20 ounces. They measure about 20 cm long or between 8-10 inches.

Around 16 weeks, your juvenile guinea pig should weigh about a kilogram or 30 ounces. The length will be between 8 and 10 inches. At 20 weeks, they weigh around 30 to 35 ounces. The length may increase to around 11 inches.

At 22 weeks, a guinea pig will weigh about 35 ounces and its length may reach 12 inches.

Guinea pigs are considered adults at 24 weeks of age.

How Big Are Full-Size Guinea Pigs?

Full-size or adult guinea pigs reach a weight of 40 to 50 ounces (2 to 4 lb.) depending on their breed. They usually measure between 10-12 inches long.

Guinea pigs stop growing around the age of 6 months or 24 weeks and are considered adults around this age.

Biggest and Smallest Guinea Pig Breed

As mentioned earlier, the Rex is the largest guinea pig breed. It measures over a foot in length and can weigh about 1200 to 1400 grams or 50 to 55  ounces or about 5 lb.

The smallest guinea pig breed is the laboratory Dunkin Hartley breed. It weighs just about 500 g or 1.3 lb. in adulthood and is used for scientific tests and research.

The Ridgeback guinea pig is also a small variety of guinea pigs. It only grows to 5 inches in length and weighs up to 2.5 lb. 

The American guinea pig is another small-sized guinea pig weighing about 2.6 lb. Skinny guinea pig, as its name indicates, is another small-sized cavy breed weighing about 2.5 lb.

Size chart (including breeds and sizes)

Guinea Pig Breeds	Baby Size	Adult Size
#1 American guinea pig	2.9 to 3.5 ounces	2.2 to 2.6 lb.
#2 White-crested guinea pig	3.5 to 4 ounces	2.5 to 3 lb.
#3 Abyssinian	3 to 3.6 ounces	3 to 4 lb.
#4 Peruvian	3.5 to 4 ounces	3.05 to 4 lb.
#5 Silkie	3.5 to 4 ounces	2.6 to 3 lb.
#6 Coronet	3.0 to 3.5 ounces	2.5 to 3 lb.
#7 Texel	3.0 to 4 ounces	2.5 to 3.5 lb.
#8 Sheba	3.5 to 4 ounces	2.5 to 3 lb.
#9 Teddy	3 to 4 ounces	2.6 to 3 lb.
#10 Skinny	2 to 4 ounces	1 to 2.5 lb.
#11 Baldwin	3 to 4 ounces	2 to 3 lb.
#12 Rex	4 to 5 ounces	2.8 to 4 lb.

Factors Affecting the Size of Guinea Pigs

The main factors affecting the size of guinea pigs are its breed, gender, the number of siblings it has, and also its diet and overall health. 

Breed: As seen above, different guinea pig breeds have differences in their weights and lengths. Some breeds like the Rex are genetically longer and larger.

Captive Rex guinea pigs can also grow very large, which is why owners must pay special attention to their diets. Guinea pigs kept for scientific studies such as the Dunkin Hartley guinea pigs are often smaller and weigh about 600g.

Litter sizes: Most guinea pigs give birth to 1 to 8 pups. If the litter size is large, then the pups will be naturally smaller.

Gender: Male guinea pigs are longer and also weigh slightly more than females.

Diet and health: The size of captive or pet guinea pigs also depends on their diet and overall health. Laboratory guinea pigs are sometimes fed very high-energy diets which could make them heavier.

Conversely, they may be fed low-fat diets to keep them smaller for research and scientific studies.

As pets, a guinea pig’s weight depends on its owner. Some piggies eat all day and could gain weight if they do not exercise.

If your pig’s diet is rich in sugary fruits like berries and other treats, then it could gain weight and become larger than normal. Certain health issues like tumors and pregnancy can also lead to larger body sizes in cavies.

Oxbow Essentials Guinea Pig Food

Conclusion – How Big Do Guinea Pigs Get?

Most guinea pigs weigh between 700 and 1400g ( 30 to 50 ounces or 1.5 to 4 lb.) at adulthood. They measure about 10-12 inches in length and up to 5 inches in height. 

Baby guinea pigs weigh between 2.5 to 5 ounces at birth. They are considered fully grown at 24 weeks or 6 months. 

The sizes of guinea pigs vary from breed to breed. Laboratory and wild guinea pigs may be larger or smaller depending on their diet, stress levels, and overall health.

Captive or pet guinea pigs could grow larger if they are fed sugary treats and do not exercise well.

We hope this guide helps you assess if your pig is growing normally.