Guinea Pig Size and Weight – How Big Do Guinea Pigs Get?

Guinea pig size can vary based on factors such as age, gender, breed, and nutrition. On average, most guinea pigs will fall within the same standard size and weight range. Baby guinea pigs start small, but they grow at an incredible speed. Throughout this article, I’ll cover baby guinea pig sizes and growth rates, as well as the factors that affect a guinea pig’s full-grown adult size.

Average Size and Weight of a Full Grown Guinea Pig

Guinea pigs are one of the largest pet rodents. Their size exceeds other common pets like rats, mice, gerbils, and hamsters by a landslide. On average, guinea pigs grow to a length of 8-12″ (20-30cm) and weigh between 700-1200 grams (1.5 to 2.6 lbs). Males are often up to 25% bigger than females. Some guinea pigs can reach up to 3lbs, but this may indicate that they are a bit overweight. Guinea pigs usually stand around 4-5″ high at the shoulders.

Male vs Female Size

As with many species, male guinea pigs are generally slightly larger than females. However, their size can overlap in many cases. Males tend to grow to the mid to upper range of average sizes, while females often reach the lower to mid-size estimates. Full-grown females usually grow to 8-10 inches and weigh anywhere from 1.5 to 2.5 lbs at maturity. On the other hand, Males typically exceed 2 lbs and can grow anywhere from 8 inches up to 12 inches long.

Some people try to sex guinea pigs by size alone. This is a very bad idea! While some males grow larger, females can grow to the same size or even bigger than most males. I’ve had multiple girls who have grown larger than many males. Size is never a reliable indication of gender.

Actual Guinea Pig Weights

To provide a more realistic picture, I created a list of several of my guinea pigs, past and present, and their average weights. I also listed breed and gender. As you can see, male vs. female weight is not always black and white.

My Abyssinians were the lightest, but this does not mean they were smaller in appearance. Abyssinians are typically the most active guinea pigs, so this helps keep their weight down. Most of the American piggies could stand to lose a couple of ounces, but they sure are stubborn about it. Such is life with guinea pigs. 😅

Ace – Male Abyssinian – 2lbs 4oz (1020 grams)

Ceico – Male American – 2lbs 6oz (1077 grams)

TJ – Male American – 2lbs 10 oz (1190 grams)

Willow – Female American – 2lbs 5 oz (1049 grams)

Daisy – Female American – 2lbs 5 oz (1049 grams)

Peach – Female Peruvian Cross – 2lbs 8 oz (1134 grams)

Poppy – Female Abyssinian – 2lbs 1 oz (935 grams)

Size Difference Between Breeds

Most breeds will fall into the average size ranges of 8-12 inches and 700-1200 grams. However, some may be more likely to hit the smaller end of the average, while other breeds typically grow to the larger end of the spectrum.

American and Texel guinea pigs can sometimes be on the smaller side as a whole.

Peruvian and Rex guinea pigs often grow to the larger end of the spectrum. Peruvians look even larger than they are because of all their hair.

Rex guinea pigs have even been known to grow up to 17 inches long! They do not always grow to this size, but they tend to be on the upper end of average guinea pig sizes.

Rex guinea pig.

Keep in mind that individuals of every breed can vary quite a bit. For example, my biggest guinea pig right now is a male American, despite them being a “smaller” breed. Getting a particular breed of a guinea pig is no guarantee that your guinea pig is going to turn out big or small.

Can Guinea Pigs Be Small?

On occasion, you’ll find individuals who grow a bit smaller than average. This is due to genetics and sometimes lack of nutrition they received while growing. Sometimes, there is a slight difference in size between breeds, but most will still fall into the average size range. There is no such thing as “dwarf” or “miniature” guinea pigs as a breed.

What is the Largest Guinea Pig Breed?

Cuy guinea pigs in Peru.

Cuys are the largest guinea pig. These monster guinea pigs can grow between 4 and 8 pounds!

In addition to their monstrous size, cuys can be identified by their smooth coat, orange and white coloring, and extreme skittishness. Cuys were originally bred in Peru as a food source.

Some made their way into America to be sold as pets. However, Cuys do not make very good pets at all.

Since they are bred to grow to unnatural sizes, their weight puts a lot of pressure on their organs. They often die of organ failure or other health problems before they reach 4 years old.

In addition, they are frantically skittish and very difficult to tame. They are also harder to handle because of their nervousness and colossal size.

Largest Rodent in the World

Did you know that guinea pigs also have a much larger cousin in the cavy family?

Capybaras are often referred to as “giant guinea pigs” because they kind of look like enormous guinea pigs.

Although they are not guinea pigs, they come from the same family of South American rodents, called the Caviidae.

Capybaras often grow to 4 feet long, and they can weigh more than 100 pounds!

Capybaras closely resemble giant grumpy-looking guinea pigs.

What is a Healthy Size for a Guinea Pig?

A healthy average weight for guinea pigs is in the range of 700-1200 grams. However, guinea pigs are individuals, and it’s hard to judge by weight average alone.

To determine if your guinea pig is a healthy weight, look at them from above and judge their body shape. You should also do a hands-on test to feel for their ribs, hips, and spine. You should be able to feel the hips and spine of a healthy guinea pig, but not the individual ribs. When looked at from a birds-eye view, the chest should be narrower than the hind end. Check out the guinea pig size-o-meter here for more information on judging your guinea pig’s body condition.

If they have no discernable shape and have feet hidden from view, it may be time to change their diet and exercise regimen. Make sure your guinea pig is getting no more than 1/8 cup of pellets per day. You can also cut down veggies to about half a cup per day. Make sure you choose high Vitamin C veggies, so your piggy doesn’t become deficient in this essential nutrient.

Exercise is also essential for overweight guinea pigs. Try to provide floor time as much as you can. Encourage your guinea pigs to exercise more in their cage. You can do this by hiding treats around the enclosure or putting their ration of pellets in a treat ball to roll around.

Is Your Guinea Pig Pregnant?

If you have a guinea pig with a discernable lump around her belly area, you may want to consider if there’s a possibility of pregnancy.

If you just got your guinea pigs, this is a possibility. Often previous owners or pet stores can sex guinea pigs incorrectly. If you have two guinea pigs, double-check their genders to be sure they’re the same.

If you’re unsure, take them to a vet to check, or ask in guinea pig Facebook groups if you’re unable to take them to a vet. Big bellies are not always an indication of pregnancy, however. Sometimes guinea pigs are simply chunky and need to go on a diet and be more active.

Guinea Pig Size Compared to Hamsters

Many people confuse guinea pigs and hamsters, but these two animals couldn’t be more different! One of the main differences is their size. While guinea pigs generally grow 8-12 inches in length and weigh 700-1200 grams, the largest hamsters will only grow to about 6 inches long and 120 grams in weight. Baby guinea pigs are a comparable size to hamsters, but guinea pigs will outgrow this size very quickly.

How to Measure Your Guinea Pig

You can measure your guinea pig by placing them on a flat surface beside a ruler or measuring tape. Get an approximate measurement from the tip of their nose to their rear. It often helps to give your piggy some veggies to munch on while you’re measuring. Most guinea pigs don’t like to sit still for too long without a food distraction.

Weighing Your Guinea Pig

It is an excellent idea to weigh your guinea pigs every week. Weight loss is often the first sign of a health problem. Sometimes it’s also the only sign of illness you will see until a condition worsens. Since guinea pigs are prey animals, they will often hide their sickness until they become much more difficult to cure.

How to Weigh Your Guinea Pig

You can weigh your guinea pig using any digital kitchen scale. It’s best to choose one that measures in different units, such as grams, pounds, and ounces. It’s also a good idea to choose one with ample surface space so the guinea pig can sit on it comfortably.

I usually give my piggies some veggies to keep them still on the scale. If your guinea pig isn’t interested in this, you can always place a large bowl or basket on the scale and put your guinea pigs in that. Just remember to subtract the weight of the bowl from the total weight calculation.

How Much Weight Loss is Normal?

At what point should you be concerned about weight loss? Small fluctuations are perfectly normal, but it’s crucial to write down the results of your weekly weigh-ins and look for patterns. The following guidelines will tell you when it’s normal and when you should seek veterinary advice. This is based on a weekly weighing schedule.

Up to 25 grams less than the previous weigh-in: Completely normal weight fluctuations

25-60 grams less: Keep an eye on your guinea pig’s weight, and weigh them more frequently

60-100 grams less: Keep a very close eye on your piggy and call your vet to set up an appointment. Weigh daily, and look for accompanying symptoms that may be cropping up as well.

100+ grams less: This much weight loss over a week is a sign of an urgent problem. Get to your vet right away.

Common causes for weight loss include infections, dehydration, dental problems, improper diet, scurvy, stress, and so many more.

Weight Gain

Regular weighing is also helpful to indicate when your guinea pig is starting to pack on some unnecessary weight. If your guinea pig is full-grown, and their weight is increasing steadily, you should probably make some changes.

Weight gain can be caused by feeding incorrect foods, too much food, or a lack of exercise. Guinea pigs are incredibly prone to obesity, so keeping them at a healthy weight can be a challenge. Be sure you’re feeding pellets that do not contain any colored pieces, nuts, or seeds. These are extremely fattening for guinea pigs. Also, avoid most store-bought treats, and limit fruit to minimal amounts.

Feed no more than 1/8 cup of pellets per day. If your guinea pig is chunky, you can cut this down even further. Also, feed a cup of veggies max each day. Provide a large cage and plenty of floor time to let your guinea pig run around.

Weight gain can contribute to heart disease, diabetes, joint and mobility problems, high blood pressure, and countless others. It can also weaken the immune system and make it harder for your guinea pig to fight off diseases if they do get sick. Keeping your piggy at a healthy weight has many benefits and can even help your guinea pig live longer.

Guinea Pig Size by Age

Baby guinea pigs grow rapidly during the first 4 months and then continue to fill out and grow slightly in the months following that stage. Below I’ll go into more detail about when and how much you can expect guinea pigs to grow by each age checkpoint.

Newborn Guinea Pigs

Newborn baby guinea pigs with mom.

Newborn baby guinea pigs range from 3-4″ (8-10cm) long at birth and weigh between 60 and 120 grams, with an average of 80 ounces. Baby guinea pigs are fully furred and can fit in the palm of your hand.

The size at birth depends mainly on the litter size. Guinea pig litters can result in anywhere from 1-6 pups, with 3 being the average number in a litter.

Smaller litters tend to have larger babies, and larger litters naturally result in smaller pups. This is because there’s less room for the babies to grow inside their mom.

This does not generally impact a guinea pig’s adult size, however. Given proper care and nutrition, they will catch up in size quickly and grow to an average adult size.

Birth to 8 Weeks

From birth, baby guinea pigs will gain 30-50 grams per week until they hit 8 weeks old. They grow incredibly fast at this stage, usually doubling in size between birth and 8 weeks. By 2 months old, baby guinea pigs are generally about 6-8″ long and weigh approximately 180-240 grams.

16 Weeks

From 8 to 16 weeks old, guinea pigs are still in the middle of a rapid growth spurt. However, it slows down a bit compared to the first 8 weeks of life. By 16 weeks old, young guinea pigs will be close to their adult length. By this age, baby guinea pigs are typically around 8-10 inches in length and weigh between 360 and 480 grams.

6 Months Old

By 6 months, guinea pigs are finished the majority of their growing. They may grow slightly bigger, but only marginally. They will, however, continue to fill out and gain weight over the next several months. By 6 months, they should move to adult food and grass hays, such as orchard or timothy hay. Avoid alfalfa hay with guinea pigs older than 6 months.

1 Year Old

Between 12 and 14 months, guinea pigs are completely done growing and have reached their adult weight. For most guinea pigs, this is anywhere from 700-1200 grams. At this point, guinea pigs are both physically and mentally mature.

You may notice their personality change by this point as well. Guinea pigs tend to chill out a lot by this age. They will popcorn and run zoomies less frequently than they did as babies.

From this point onwards, it’s even more important to keep an eye on your guinea pig’s weight. Guinea pigs are prone to obesity and gain weight very easily once they hit maturity.

Proper Nutrition for Growing Guinea Pigs

Baby guinea pigs that are in the midst of a fast-growth spurt need extra calcium and other nutrients. They need most of these nutrients in the first 4-6 months of their life. Guinea pigs that don’t receive enough nutrients from their diet during this time can suffer deficiencies and stunted growth.

From 4 weeks old up to 16 weeks, baby guinea pigs will be weaned off their mom’s milk and amid the most significant growth spurt of their lives. During this period, it’s essential to provide them with plenty of calcium-rich foods.

One way you can do this is by providing them with pellet food formulated for young guinea pigs. Alfalfa hay is higher in calcium than regular grass hay, so this is also suitable to feed.

However, if you are housing your baby guinea pig with adults, you do not want to feed either of these. High calcium can cause bladder stones in full-grown guinea pigs. This is a severe, painful condition that requires surgery and can be life-threatening.

Another way to provide calcium is to feed the baby some high calcium veggies separate from the other guinea pigs. Check out this article on 21 high calcium veggies to feed your guinea pig for some ideas.

Young guinea pigs will need calcium up until they turn 6 months old. They require less between the ages of 4-6 months, as most of their growth occurs by the 4-month mark. Once guinea pigs turn 6 months old, they no longer need extra calcium in their diet. They should also have access to unlimited grass hay, such as timothy or orchard grass hay.

Guinea pigs of all ages need Vitamin C in their diet, and growing babies often need more of this essential nutrient. Unlike calcium, guinea pigs cannot overdose on Vitamin C. The best way to provide Vitamin C is to feed bell peppers daily. You can also supplement with Oxbow’s Vitamin C tabs.

What Can Cause Stunted Growth in Guinea Pigs?

A few factors can impact your baby guinea pig’s growth rate. Health and nutrition are a couple of big ones. If babies don’t receive enough nutrients while growing, this can cause their growth rate to slow down. If they are deficient for a length of time, this can cause them to be significantly stunted.

To prevent this, make sure your young guinea pig is eating plenty of hay, high-quality pellet food, and a variety of fresh vegetables. Calcium and Vitamin C are two of the most essential nutrients for growing guinea pigs.

Illness can also impact growth. If a baby guinea pig gets sick, the body puts more energy into healing and getting healthy again. This can cause a temporary or permanent stunt in growth depending on the length and severity of the illness.

To decrease the chances of your baby guinea pig getting ill, provide a proper diet and a large, clean cage. Make sure they’re located in a well-ventilated space free of drafts. Avoid using harsh chemicals or cleaning sprays near your guinea pig’s cage.

Genetics can also cause guinea pigs to grow smaller or larger than usual. You can generally get a good idea of your baby guinea pig’s future size by looking at their parents.

In Conclusion

Guinea pig sizes can vary, but most guinea pigs will fall within the average range of 8-12″ long and 700-1200 grams in weight when fully grown. Although baby guinea pigs may start out being the size of a hamster, they will grow rapidly. Most guinea pigs approach their adult length by only 16 weeks old.

Guinea pigs are very large compared to other pet rodents, and they have a much longer lifespan. Some can even rival large breed dogs with lifespans into the double digits! To learn more about how long guinea pigs live, check out this article on guinea pig lifespan.