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When Does a Guinea Pig Stop Growing?

Guinea pigs have become very popular pets due to their playfulness and small size.

Tracking your guinea pig’s weight is important to ensure your pet grows properly.

Guinea pigs have a rapid growth rate until they reach their adult size, but once fully grown, they need to be monitored to prevent obesity.

But how do you know when your guinea pig has stopped growing?

Generally, a guinea pig is considered an adult at six months old, but the animal will not stop growing until it is about 14 months of age. After 14 months, a guinea pig will not grow in length, and any increase in size will be in gaining weight.

A baby guinea pig will measure 3-4″ inches in length and weigh 0.15-0.25 pounds at birth, but once fully mature, it will grow between 8-12″ inches long and weigh 1.5-2.6 pounds.

If your guinea pig is older than 14 months and weighs more than 2.6 pounds or less than 1.5 pounds, it is best to consult a veterinarian to evaluate your pet’s health and diet.

Read on to learn more about what affects a guinea pig’s size and how to ensure your pet is healthy.

when does a guinea pig stop growing

What Affects the Size of a Guinea Pig?

Male guinea pigs are typically larger than females, but several other factors affect their overall size.

A poor diet, small cage, and lack of companionship will affect your cavy’s growth rate and negatively impact the animal’s health.


A healthy, balanced diet with essential vitamins and minerals supports healthy growth in guinea pigs.

Guinea pig teeth keep growing throughout life, and you will need to provide your pet with plenty of hay and leafy green vegetables to keep the teeth worn down and maintain dental health.

Low-calcium Timothy hay is an excellent choice, along with leafy greens such as broccoli, spinach, and cabbage.

Guinea pigs cannot produce their own vitamin C, so the animals must receive the nutrient from their diet.

Cavies need 10-50 milligrams of vitamin C daily to support healthy skin, joints, and gums.

Guinea pig pellets fortified with vitamin C and plenty of leafy green vegetables will provide your pet with this essential nutrient.

A guinea pig also needs a constant supply of fresh, clean water for proper hydration and digestion.

You may give your cavy treats but do so sparingly to avoid excessive weight gain.

Without the proper nutrients, a cavy will experience stunted growth and malnourishment.

Likewise, too many treats or high-calorie foods may cause your guinea pig to become overweight.

Ensuring your cavy has a nutrient-rich, balanced diet along with adequate exercise will keep your pet at a healthy weight.

Cage Size

The size of a guinea pig’s cage also impacts its weight and overall health.

Keeping your cavy’s environment clean by regularly removing rotten food or soiled bedding will lower the risk of diseases caused by harmful bacteria.

A large cage with plenty of toys will ensure your guinea pig is mentally stimulated and can get plenty of exercise.

A cavy may become bored in a small enclosure, causing the animal to change its eating habits or become ill.

When a guinea pig is unhappy in its cage, it may sleep more often and become disinterested in food altogether.

As stated in the previous section, a balanced diet and adequate exercise are vital to maintaining a healthy weight and preventing disease in guinea pigs.


Guinea pigs are social animals, and studies have shown they are healthier when they have a cage mate to spend time with.

Without a companion, a cavy may have increased stress levels.

Too much stress will cause a guinea pig to have a poor appetite, which results in slower growth.

Providing your cavy with a companion will reduce the animal’s stress and prevent feelings of loneliness.

When you keep a male and female guinea pig together, they should be neutered or spayed to prevent unwanted breeding.

For two cavies, you will also need a cage size of at least 10.5′ square feet, so each animal has its own space and does not become territorial.

Related: Combining Three Or More Guinea Pigs In One Cage.

Guinea Pig Growth Chart

It is crucial for guinea pig owners to weigh their pet as it goes through the stages of growth to know if their pet is reaching weight milestones.

A rough idea of how much your cavy should weigh at each growth stage ensures your pet is growing properly.

Cavies at birth will measure between 3-4″ inches, and they experience a rapid rate of growth from when they are born until they are eight weeks of age.

A guinea pig’s growth slows significantly between 14-16 weeks of age, but they will continue to gain weight.

Use a kitchen scale to weigh your guinea pig, and place a paper towel underneath the animal so it has a better grip and feels more secure.

The following table shows the average guinea pig weight and length for males and females from 8 weeks to 14 months.

Guinea Pig AgeMale LengthMale WeightFemale LengthFemale Weight
8 weeks7” inches210 grams7” inches210 grams
10 weeks7.5” inches260 grams7.5” inches260 grams
12 weeks8” inches300 grams8” inches300 grams
4 months8.5” inches420 grams8.5” inches400 grams
5 months9” inches540 grams9” inches500 grams
6 months9.2” inches660 grams9.2” inches600 grams
7 months9.4” inches720 grams9.4” inches625 grams
8 months9.6” inches780 grams9.6” inches650 grams
9 months9.8” inches840 grams9.8” inches675 grams
10 months10” inches880 grams10” inches700 grams
12 months10-12” inches950 grams10” inches750 grams
14 months10-12” inches1100 grams10” inches800 grams

Do Guinea Pigs Come in Different Sizes?

The size of guinea pigs will vary because of their genetics, diet, body composition, and amount of exercise they receive.

Male guinea pigs of all breeds are generally larger than females.

Female guinea pigs typically give birth to between 3-6 babies, with a larger litter resulting in smaller offspring.

However, the largest variation in size will occur when comparing different breeds of guinea pigs.

The American Cavy Breeders Association currently recognizes 13 breeds of guinea pigs, all of which come in varying sizes.

Some breeds of guinea pig, such as the Rex, grow much larger than the average cavy, reaching lengths up to 17″ inches when fully mature.

Breeds like the Texel and the American guinea pig are slightly smaller than average, with a length ranging between 8″ and 9″ inches.

Further Reading: Guinea pig pedigrees and types

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