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How Big Do Guinea Pigs Grow? [Average Size Information Guide]

Guinea pigs are known to be small pets, but they grow relatively quickly. Due to this, many people wonder if their guinea pig is a healthy weight and size. This post will include everything you need to know about your guinea pigs size, now as a pup and as a full grown boar or sow.

So how big do guinea pigs grow? The average female guinea pig weighs anywhere from 900– 1100 grams. She stands 8 – 10 inches tall. The average male guinea pig weighs 1000 – 1200 grams. He stands at 8 – 12 inches tall.

Of course, guinea pigs do not always grow to this weight and size. So, it is very helpful to track these measurements and compare them to averages of other guinea pigs that owners have seen.

This post will also include the average weight and heights of guinea pigs across their full life cycle.

Growth of Guinea Pigs

Guinea pigs are quite unique from other pet rodents because they grow a lot larger than the likes of mice, rats, and hamsters. They grow very rapidly and you can expect them to soon double in size months after they are first born.

Guinea pigs are born as part of a litter. Each litter typically will contain Guinea Pig pups that vary in size and weight. Some pups will be quite noticeably bigger than others and the average size will depend largely on how many pups are born as part of that litter. So, a small litter will generally produce larger pups. This is not to be a concern, it is completely normal.

Litters usually consist of 1-6 pups, with the average being 3 babies each time.

Guinea pigs will grow to around 15-20 cm (6-8 inches) within 8 weeks of birth. Beyond this, growth seems to stall, but they will still reach 20-25 cm (8-10 inches) in around 16 weeks.

Interestingly, guinea pigs don’t reach their full grown size until they are around 14 months of age. They are around 20-30 cm (8-12 inches) at this point. At this stage they are fully grown and you should not expect them to get any bigger

Here is a table that includes the average weight and height over the first 14 months of Guinea Pigs.


Age of Guinea PigAverage Weight in Grams
Birth60-120 Grams
8 Weeks180-240 Grams
16 Weeks360-480 grams
14 Months1000-1200 Grams


Age of Guinea PigAverage Size in CM/Inches
Birth8-10cm (3-4 Inches)
8 Weeks15-20cm (6-8 Inches)
16 Weeks20-25cm (8-10 Inches)
14 Months20-30cm (8-12 Inches)

As we can see in the table, a guinea pigs growth starts from an early age and you don’t need to worry thinking that this will continue. Trust me, this fast growth does stall down.

The biggest growth spurt will occur in the first 8 weeks of your guinea pigs life, but that won’t be all of it. During this time, it is normal for your guinea pig to gain a couple of grams of weight each day!

When your guinea pig is 7 months old you can estimate their weight by doubling their current weight.

This is because by this stage they will likely have hit 50% of their total weight and full weight.

What Contributes To Guinea Pig Size?

We’ve already touched on the size of a guinea pig at birth. Whilst it varies here, depending on the litter, guinea pigs will ultimately ‘catch up’. Therefore if your guinea pig was smaller due to the fact that they came from a larger litter; they tend to grow faster than a guinea pig from the opposing context.

Ultimately, it just depends on whether the growth is experienced inside or outside of the pregnant mother.

Outside of birth, one of the biggest factors that contribute to your guinea pig’s ultimate size will be the size of their parents. If you average the height and weight of your cavies parents, that will be pretty close to what your pup will look like when he or she grows up.

Your guinea pigs diet and activity level are also important to how ‘big’ they ultimately will grow. You of course want them to be at a healthy weight and not to obtain much excess weight for their frame to carry.

Quality food and regular exercise are important for guinea pigs, just like any other animal.

You need to keep treats to a minimum, and to not feed them too regularly. When it comes to food, opt for a high quality feed that is abundant in fiber, vitamins and minerals.

The Kaytee brand on Amazon is excellent because it contains everything your guinea pig will need including vitamin C, pre-biotics and pro-biotics.

You will never be able to know for certain exactly the size and weight of your guinea pig. We can only go on estimates and averages. However, these do tend to be rather accurate and you do not usually come across too many outliers.


Measuring the size of your guinea pig and their weight is advised throughout their life. It can be a good indicator that they are being fed enough (and not too much) and it can help you determine if they are growing as they should.

To measure the size of your guinea pig, you can use a tape measure. To begin with, place your guinea pig on a flat surface and use the measuring tape alongside to identify their length.

When measuring, you will want to go from nose to rear. This is the industry standard for guinea pigs as used by veterinarians.

This measurement does not need to be precise. You’ll likely find your guinea pig moving around a lot anyway making this almost impossible. Nonetheless all you are looking for here is a general measurement.

Accompanying their size, will also be their weight. Weight generally coincides with the size of your guinea pig.

It comes as no surprise to learn that a larger guinea pig is a heavier one. Consider that female guinea pigs (sows) will weigh slightly less than a male guinea pig.

Its important to regularly weigh your guinea pig, to ensure they fall within the healthy range. To do so, you can get a scale that was purposely designed for pets and makes the whole process much easier.

Final Words

While guinea pigs and other animals will always vary in size, they do normally conform with the averages as provided in this guide.

You should always remember that the information provided here are general averages, and not specifically finate.

If your guinea pig’s size is slightly above or below the numbers given here then there is no cause for alarm.

However, if you notice that your guinea pig is quite a lot different its a good idea to take them to your vet. It could indicate a potential health concern. This is why measuring and weighing your guinea pig regularly is thoroughly recommended.