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How Big Can Koi Fish Get? Growth Rate & FAQs

Lindsey Stanton Profile Picture

By Lindsey Stanton

koi fish

Koi fish are definitely some of the coolest fish that you can get for a backyard pond. They may not be the easiest to care for, and they certainly are not cheap, but they are well worth the investment.

They help create a beautiful pond scene that everybody can enjoy. However, people have been asking us questions about their growth, specifically their size, how fast they grow, and more. So, how big can koi fish get and how fast do they grow?

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How Big Do Koi Fish Get?

When it comes to the size of Koi fish, they are some of the larger types of domesticated fish that people tend to own. Now, they are a little too big to have in aquariums, at least if you don’t want to turn half of your home into a fish tank, yet they are perfect for outdoor ponds, or even for indoor ponds too.

Now, a normal average Koi fish will grow to around 15 inches long, or at least 1 foot at a minimum, which is 12 inches. These are the kind of Koi fish that are best suited for home aquariums due to their relatively small size. This is not the only kind of Koi, though. There are also Japanese Koi, which can grow between 22 and 26 inches in length. This kind of Koi would not usually be found in indoor aquariums due to its size.

The other kind of Koi is the Jumbo Koi fish, which can grow up to 36 inches or 3 feet in length. Some of these jumbo Koi, the record breakers, have gotten as long as 52 inches. These guys are big and they are best housed in outdoor ponds due to their fairly large size. As you can see, how big a Koi fish can get does actually depend on the specific type of Koi that you are looking at.

koi fish in pond
Image Credit: Dpongvit, Shutterstock

How Fast Do Koi Fish Grow?

Generally speaking, it will take your average Koi fish about 3 years to reach its full length. Now, the smaller varieties grow a little faster and may reach their full size in 2 years or less, but these are the smaller ones.

Japanese and Jumbo Koi fish can take up to 3 years to reach full size. Your average Koi should be around 8 inches long by the end of its first year of life, with the rest of the length being achieved over the following years.

starfish divider ahHow To Maximize Koi Growth

There are some things that you can do to ensure maximal and fast Koi growth. There are a few factors to keep in mind here, all of which will make a difference in terms of helping your Koi fish achieve its maximum potential size. Let’s talk about how you can make sure that your Koi fish grows big, healthy, and quickly too.

Proper Feeding

The first and most important thing to help your Koi grow big and fast is to feed them the right foods. Koi fish have pretty fast metabolisms and they need a fair amount of food. You should feed them 3 times per day, but no more than they can eat in 5 minutes per feeding.

You do not want to over or underfeed these fish as both will affect growth. Also, when the water is very cold or hot, you want to stop feeding due to metabolic issues.

Now, of course, the amount of food is not the only factor here. The type and quality of the food your feed your Koi matter as well. Koi need lots of protein, and in fact, most of their diet should be protein-based, specifically meat protein.

Yes, you can use high-quality Koi flakes or pellets, but these are not the best. You should alternate that stuff with fresh and live foods like insects, insect larvae, other small fish, worms, and other such things.

A Good Pond (Size)

Like many fish out there, a Koi’s growth will be partially determined by the tank or pond that you have it in. If the tank or pond is not large enough to sustain the full length and size potential of the fish, it will most likely never grow that big to remain comfortable in the space it has. No, this is not a conscious decision, but it is the reality nonetheless.

A full-sized 36 inch Jumbo Koi fish requires around 50 gallons of pond water that is 3 feet deep. The more fish you have, the deeper and larger the pond needs to be. For instance, for 3 full-sized Koi fish, a pond that is around 4 or 5 feet deep, and between 150 and 200 gallons is ideal.

This will allow the fish to feel at home, to have lots of space, and to reach their full-size potential.

Image Credit: Vital Safo, Shutterstock

Proper Filtration

Another really important thing to keep in mind if you want your Koi fish to grow big and strong is water quality. If the quality of the water is not good, it will create stress for the fish, plus it will make them unhealthy, sick, and could even kill the Koi too.

Now, Koi are pretty hardy and resilient, but this does not mean that they don’t do better in clean water than in dirty water. Clean and well-filtered water is always the best no matter what kind of fish you have. Therefore, you need to get a good filtration unit, one that engages in all 3 major types of filtration.

This includes mechanical filtration to remove solid debris, biological filtration to remove ammonia and nitrites, and chemical filtration to remove other toxins, odors, and colors. Also, a good filtration unit for Koi fish should be able to process between 3 and 5 times the total amount of water in the pond per hour.

So, if you have a 100-gallon pond, the filtration unit should be able to handle 300 gallons per hour at least, if not closer to 500 gallons per hour, which would be ideal.

Ideal Water Conditions

While Koi fish are quite resilient and adaptive, providing them with their ideal water conditions to live in will also help maximize their growth. First off, a pH level between 7 and 7.5 is ideal for Koi fish.

Also, a water temperature of 70 degrees is ideal, with a water hardness level of around 80 ppm is good. If you keep the water within these parameters, your Koi fish should grow really well. It’s also a good idea to ensure you regularly test your water to ensure the conditions are correct (more on test kits here).

Note: we have also covered a detailed guide on caring for Koi eggs, you can check it out here.

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Final Thoughts

There you have it, all of the info you need to make sure that your Koi fish reaches its maximum potential size. As long as you feed it right, give it lots of space, and make sure that the water conditions and parameters are ideal, you should have a big, healthy, and happy Koi fish in no time at all.

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Featured Image Credit: Tanpimon Paksai, Shutterstock

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