How Big Do Guinea Pigs Get?

Knowing what size your pet guinea pig will grow to is critical in managing their health, lifestyle and enclosure. In this article, we will crunch the numbers and explore how the factors of sex, age and breed will affect your pet’s expected size.

Additionally, we’ll check the statistics on several common guinea pig breeds, including the Abyssinian, Teddy, Ridgeback, Peruvian, Himalayan and Crested.

Let’s get into it!

The Factors That Influence Guinea Pig Size

Lifecycle, sex and breed will all affect the size of your guinea pig. The size of domestic guinea pigs ranges from 1-3 lbs in weight and 12 inches long — but there are some exceptions. 

Let’s break down all those factors to understand better what you can expect from various guinea pigs.

The Weight Difference Between Male and Female Guinea Pigs

Boars (male guinea pigs) can be expected to grow a little larger than sows (female guinea pigs). Adult boars will weigh between 2-2.6 lbs. Sows, however, will normally reach an adult weight of 1.5-2 lbs.

Pups of both sexes, at birth, will weigh about 3.5 oz. The pups will be twice that length by 8 weeks of age. This is the fastest and most significant period of growth in a guinea pig’s life cycle.

The Changing Sizes of Different Guinea Pig Breeds

The biggest guinea pigs are the ‘Peruvian Breed.’ These incredible livestock guinea pigs were bred through a joint Peruvian government and farmer initiative. 

The Rex is another giant among guinea pig breeds. An adult Rex can grow to an intimidating 17 inches long. Most guinea pigs will struggle to reach even half the length of an adult Rex. Many domestic owners of guinea pigs fancy the smaller breeds. 

The American guinea pig is the smallest. Adults of the American breed commonly grow to about 8-9 inches in length. 

Though slightly larger than the American, the Texel is another tiny breed. Your average Texel will, in adulthood, measure between 8-10 inches in length. 

The average length of a guinea pig, across all the breeds, comes to about 12 inches. 

How Quickly Do Guinea Pigs Grow?

Size is a great way to estimate a guinea pig’s age. It’s also good to have a general idea of what your guinea pig ought to weigh for veterinary reasons. 

???? Newborns

Newborn guinea pigs look like tiny tangerine-shaped balls of adorableness. They generally weigh from 2.1-4.2 oz, with an average length of 3-4 inches. These guinea pups have a lot of growing to do before they can be adopted. Most guinea pig owners will never even see a pup this tiny. 

For the next eight weeks, your guinea pig will grow at an incredible rate — normally doubling in length.

???? 2 months

At 2 months old, your guinea pig has completed the most remarkable period of growth in their lives. 

After the eight-week mark, a guinea pig’s growth will slow — but not plateau. Most guinea pigs still have a good four weeks of less rapid growth. Many guinea pig breeders are happy to home their guinea pigs at 6 or 7 weeks old. 

???? 3 months

Owners can observe the next period of growth as the guinea pig ages three months. At this point, most guinea pigs will be 7-9 inches long and weigh 8.5-13 oz. After this, you can expect your guinea pig to continue gaining around 1 oz of monthly weight. 

???? 6 months

A 6-month-old guinea pig will have gained very little length, but quite a lot of weight. At six months, your average guinea pig will have reached a total weight of 17-25 oz.

???? 1 year

Your guinea pig will have a sturdy and adult appearance at 1 year old. The skeleton of your guinea pig will have met its maximum growth potential at this point. A 1-year-old guinea sow will weigh, on average, 23-30 oz (almost 2 lbs). 

???? After 1 year

Guinea boars weigh somewhere in the range of 1-3 lbs after their first year of growth.

Not all guinea pigs grow according to this general plan. Some mature sooner, some later. Either way, by 14 months old, most guinea pigs have grown to their final adult weight and length.

Final Thoughts

Guinea pigs have pretty significant variations in size and weight across different breeds. Sensible guinea pig owners should familiarize themselves with the life cycle and growth rate of their breed of guinea pig to ensure they live long and happy lives.