How to Tell Your Guinea Pig’s Age?

Guinea pigs are great as pets because they’re a lot easier to maintain as compared to cats and dogs.

They’re a part of the Caviidae family of rodents and usually live up to 5 to 7 years.

They grow very quickly making it difficult for you to measure their age if you’re a novice pet owner.

If you don’t know much of their history, a few factors can help you determine how old they are.

Size as an Indicator of Age

Guinea pigs used to be much larger in the past. But due to unusual breeding habits, where too many people are breeding from underage animals, they are starting to grow a little bit smaller than what they used to be.

Measuring the size of your guinea pig can help you get a more accurate estimate of their actual age.

Grab a ruler or a tape measure and place your pet on a flat surface. Keep the ruler parallel to its body and measure from the tips of its nose to its rear.

Don’t try to force your cavy to stay still if it’s moving around a lot. You just need a rough estimate, not the exact measurements.

At Birth

Newborn guinea pigs are about 3 to 4 inches in size but there can be a variation among the animals in a litter.

If the litter is larger than usual, then the young guinea pigs might be smaller in size because they had lesser room to grow.

Litter size can be anywhere from 1 to 6 babies, but a typical birth produces 3 newborns at a time.


Guinea pigs grow at a rapid rate and can double in size (about 6 to 8 inches) within 8 weeks after birth.

It takes them only 16 weeks to reach around 10 inches, but after this stage, their growth slows down.


Even though their growth process becomes a lot slower, it can take them about 14 months to fully reach their potential height.

They can reach up to 12 inches. They will not get any bigger after they’ve completely matured.

Weight as an Indicator

In addition to physical size, you can measure your pet’s age by its weight. It can get bigger and heavier as it matures.

The weight varies from breed to breed as some can be naturally heavier than others.

All you need is a kitchen scale to weigh your furry companion. Place it on the scales, let it settle down and then take the reading.

You can place it in a tiny bowl if it doesn’t stay still. Make sure to subtract the weight of the bowl from the final reading to get an accurate result.

At Birth

Newborn guinea pigs can weigh anywhere from 60 to 120 grams.

It’s completely natural for some to weigh heavier than others depending on the size of the litter.

If one of the pups is significantly lighter than the rest, then you need to keep a watchful eye on it and monitor its health closely.


The guinea pigs start getting heavier each week as they grow and mature. They can gain 30 to 50 grams every week until they reach adulthood.

After growing for up to 12 or 14 months, their weight gain will start to decrease.

Male adults are known to gain about 20 to 25% more weight than female adults.


After they’ve completely grown, male guinea pigs should weigh around 900 to 1200 grams and females should be about 700 to 900 grams heavy.

If your pet weighs a lot heavier or lighter, then you need to consult a vet immediately.

Pregnant Guinea Pigs

Pregnant guinea pigs get a lot heavier during the gestation period.

This period spans 59 to 72 days. It’s pretty common for them to get twice as heavy as their normal weight.

But even so, you need to keep an eye on them to make sure everything goes smoothly,

Why You Need to Track Their Weight

Guinea pigs are great at hiding their illnesses because their strong survival instincts require them to not show any sign of weakness.

As a result, they can disguise their illnesses for a long time.

If you notice a sudden difference in their weight or that they’re not getting heavier during their growing stages, then there must be something wrong with them.

Measure their weight every week to stay on the safe side.

If you’re particularly concerned that there’s something wrong, keep a track of its weight on a spreadsheet.

This way, you’ll be able to spot any unusual or abrupt changes and take it to a vet for an examination.

Guinea pigs that are ill need to be monitored daily instead of on a weekly basis so you can notice any signs of improvement or recovery.

Other Signs of Growth

Aside from their size and weight, guinea pigs show other signs of growth if you look at them closely.


Unlike cats and dogs, a guinea pig’s teeth aren’t the best way to determine its age.

But you can notice a couple of changes in the color and texture as they grow.

A guinea pig at birth has a small set of white developed teeth. But after some time, they start turning yellow and become rough or crooked.

Occasional breakage is also completely natural.


The toes of a guinea pig start curling upwards or to the sides as they age.

Cutting the toenails can be really difficult and you have to be really careful so that you don’t cause accidental bleeding.

Clipping their nails is an important part of their grooming process because these nails can easily grow into their footpads and cause extreme discomfort to them.


Just after birth, your pet may have short pointy nails.

They are almost translucent. After it turns a year old, the nails get thicker and rounder and become opaque yellow.


The rear ends of female guinea pigs can grow wider as they age, especially after they’ve given birth.

The testicles on males become noticeable after they turn 6 weeks old.

Guinea Pig Equivalent Age to Human Time

If your guinea pig has given birth to a litter in front of your eyes, then you can easily measure the newborns’ equivalent age with respect to human time.

After 3 months of birth, they’re already 2.5 years old.

Then 6 months later, they turn 5 years old, and within a year, they turn 10.

After this, their age remains consistent with human time. At 2 years they’re 20 years old, at 3 years they’re 30, and so on and so forth.

Handling Guinea Pigs When They’re Growing

The size and weight of guinea pigs makes them a lot easier to handle, especially for kids.

They’re very friendly and usually love being petted or stroked.

Unlike other rodents, their size doesn’t allow them to curl up in small places that are difficult to reach.

Cage Size Matters

You need to purchase a cage with enough space for them to move around after they’ve fully matured.

Larger enclosures give them enough room to exercise which can prevent them from developing illnesses like heart disease or diabetes.

Frequently changing the cages as they grow can disrupt their lifestyle as they’re not used to unfamiliar surroundings and they may take a while to adjust.

If you’re getting a single guinea pig, then 30’’ by 36’’ is a good cage size.

Bottom Line

If your guinea pigs vary a little bit from the average weight or size, then that isn’t usually a cause for concern.

But you should still monitor their health regularly. Some guinea pigs may show early signs of aging and that’s also totally normal.

If you’ve had your pet for a couple of years, then chances are it’s nearing its end.

 A senior guinea pig starts losing muscle tone and gets lighter.

It can also develop osseous metaplasia or cataracts in its eyes.

It can also start becoming less active as it grows older which means you won’t find it popping up and down as much anymore. Dental problems and other medical conditions are not uncommon in their old age either.

These fun creatures are ideal for you when you’re a fairly new pet parent.

They’re very social and can keep you company for a long time.

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