Being part of the rodent family, guinea pigs are pretty unusual when it comes to size and weight.
They are noticeably bigger than their hamster, rat, and mice cousins.
The normal development of guinea pigs can be monitored by keeping track of the pet’s weight over time.
You cannot always expect clear symptoms when something is wrong, so growth rate is an important indicator of the wellbeing and health of a young guinea pig.
The weight and size can also be used to see whether the guinea pups are developing normally.
Although you don’t need to measure their size once they are fully grown, keeping track of their weight is recommended for a lifetime.
It’s not a big deal to weigh a guinea pig since all you need for this action is a set of kitchen scales and goodwill.
Once your place the cutie on the scale wait a bit for him to settle down and record the reading.
You can enter the data in a notebook or a laptop.
For those guinea pigs that can’t stay at one place or get scared in unusual situations, you can use a bowl where you will place them while measuring their weight.
Subtract the weight of the bowl for accurate readings!
Without further ado let’s dive into the growth rate of guinea pigs and what you can expect from your piggy height and weight wise!
Guinea Pig Growth + Weight Chart by Age
When we express the size of guinea pigs we put their lengths, rather than their height in mind.
You can measure the size of a guinea pig by placing a ruler on a flat surface, parallel to his body.
The size is the length from the tip of the nose to the rear.
It’s a perfectly natural thing for the weight and size to differ between different breeds and litters of guinea pigs.
Usually, a larger litter will produce lighter pups so it’s not unusual at all for a guinea pig to turn out smaller when he’s coming from a large family.
The numbers on the chart are average estimates.
You can compare your guinea pigs’ weight and size to the content in the table, but if your pet doesn’t fall in the middle it doesn’t necessarily mean there is something wrong.
If the animal eats normally and acts normally you can consult your vet whether there might be a problem and schedule a check-up if needed.
Factors such as nutrition, genetics, hygiene, and housing can affect growth in guinea pigs so put all those things into consideration while evaluating your pet’s progress.
What is the Growth Rate of a Guinea Pig?
At birth, baby guinea pigs can weigh between 2.1 and 4.2 oz (60 and 120 grams) and have an average size of 3-4 inches (8-10 cm).
Their shapes are very cylindrical-like and can be compared to tangerines in body appearance.
8 weeks after birth the guinea pig pups double their size by adding 3-4 inches (8-10 cm).
This is the period when the growth rate is very rapid. Their weight and size increase consistently and gradually.
They continue to grow at a slower rate after the 8th week, but start to appear significantly large in a short period.
During the next 4 weeks, a normally growing guinea pig gets just a bit longer.
If you didn’t plan on seeing little Fluffy transforming to big Fluffy this fast make sure you have the appropriate housing conditions.
Guinea pigs kept in a small space have weaker immune systems and this can affect their growth rate.
If you want to know more about what housing conditions guinea pigs can best live in then check out our guide on DIY guinea pig cages.
2 Months Old Guinea Pig
When a guinea pig is 2 months of age he already finished the most intense growth spurt.
You can expect an average size of 3-4 inches (8-10 cm) and an average weight of 6.3-8.47 oz (180-240 grams).
Their physical development slows down a bit. Guinea pig breeders let the guinea pups go to new homes a week or two before they reach 2 months of age.
When you decide to buy a baby guinea pig you can assume the animal’s age according to its size and weight.
Even pet store staff can sometimes be unsure about the animal’s age so you can use your knowledge to avoid buying too old or too young guinea pigs.
3 Months Old Guinea Pig
At 3 months of age, a healthy guinea pig is expected to have 8.5-12.7 oz (240-360 grams) of body weight and 7-9 inches (18-23 cm) of body length.
6 Months Old Guinea Pig
When guinea pigs are half a year old their bodies are at a point when they are already big and strong, but continue to grow slowly until full maturity is reached.
The monthly addition to their body weight is approximately 1 oz (25 grams).
The weight of the guinea pig at 6 months of age can be anywhere between 17.6-24.7 oz (500-700 grams) and the length has increased barely by an inch (2.7 cm) compared to 3 months ago.
Average Weight of a 1-Year-Old Guinea Pig
Guinea Pigs reach their full skeletal size just before they become 1 year old.
The average weight of female guinea pigs at one year of age is 23-30 oz (650 to 850 grams) and for males, it varies between 30-41 oz (850 and 1150 grams).
What Age Are Guinea Pigs Fully Grown?
Different guinea pigs finish their growth at different stages of their lives.
It’s safe to say that most guinea pigs reach their adult weight at 14 months of age.
A female guinea pig weighs approximately 25% less than an average male at this point.
Some guinea pigs continue gaining weight for a few more months.
In some cases, this happens as a continuation of the growing process, but sometimes it’s just the guinea pig getting obese.
In the past, the fully grown guinea pigs were much larger than the ones we know and love today.
The size altered over time because too many guinea pigs have been bred from a very young age.
How Big is a Full-Size Guinea Pig?
A full-size guinea pig is 8-12 inches (20-30 cm) in size.
There are extreme cases of overgrowth and undergrowth that only affect the way the guinea pig looks, nothing else.
A guinea pig that hasn’t reached its full potential even after the age at which they stop growing can be considered a dwarf.
Dwarfism in guinea pigs hasn’t been thoroughly researched and the American Cavy Breeders Association doesn’t recognize it.
There isn’t a breed of guinea pigs that can be considered a dwarf-breed, so never buy a cavy advertised as a dwarf.
Biggest Guinea Pig in the World
The Rex guinea pig is recognized as the largest guinea pig breed in the world.
Its size can reach an astonishing 17 inches (43 cm). There isn’t a single breed that even comes close to the Rex.
One of the most popular breeds is called the Abyssinian and fits in the average range of 8-12 inches (20-30 cm).
The American guinea pig, as a comparison, has a length of 8-9 inches (20-22 cm) in adulthood.
Phoberomys pattersoni is the biggest guinea pig individual and its millenniums-old remains were discovered in Venezuela.
This enormous creature weighed 1.543 pounds (700 kg) and was 1.4 yards (1.3 meters) high.
Scientists are still wondering how the modern guinea pigs got so small.
What is a Healthy Weight for a Guinea Pig?
A healthy weight for a fully grown female guinea pig is about 28 oz (800 gr) and 39 oz (1100 gr) for a male.
If your fully grown or developing guinea pig comes close to the average written in the chart it means that it probably has a healthy weight.
Weights above or below the average don’t necessarily mean problems with growth, diseases, malnutrition, or a case of overweight.
For adult guinea pigs a regular weigh-in can tell you whether your pet is packing extra weight or losing some.
It’s recommended to do this once a week.
When you notice a significant decrease or increase start measuring the weight daily or talk to your vet about the steps you need to take.
When the contours of your guinea pigs’ body are visible it’s possible to get extra information about his condition by observing the animal from above.
An ideal guinea pig body condition is when the ribs are not prominent, there is no abdominal curve and the chest is smaller than the bottom.
In overweight guinea pigs, it’s harder to see the feet and the underbelly is touching the floor.
Very thin guinea pigs have prominent ribs and their hips and spine can be felt with a slight touch.
It’s not always possible to tell if a guinea pig is overweight according to their physique because most of them appear like furry potatoes and some just have too much hair on them.
Don’t exclude the possibility of your female guinea pig being pregnant instead of getting overweight.
Sows get a lot heavier during the gestation period which lasts around 2 months.
If you have more than one guinea pig in the same cage and you are not sure of their sexes always consider pregnancy.
Even if you have the only one you bought recently, pet shop pregnancies in guinea pigs are not uncommon at all.
