How Big Do Koi Get & How to Make Koi Grow Bigger

Koi fish are popular for their large size and colorful body. In fact, koi is one of the largest fish that people stock in their pond.

But, how big do koi fish get?

On average a koi grow about 20 to 24 inches in length and weighs 9 to 12 pounds. But some koi can even bigger in length and weight.

In this article, you will learn about the size of different types of koi, things that affect their growth and how to grow larger size koi.

How Big Do Koi Get

The size of a koi depends on a number of factors like its genetics, food, water quality, their population in pond and environment.

Domestic Koi

Domestic KoiDomestic koi has the least growth among all koi verities. They usually grow from 12 to 15 inches long.

The main reason behind the smaller size is their genetics. Also, it doesn’t become possible to take the same care that a koi farm can.

Japanese Koi

Japanese KoiJapanese koi are popular for their size and color. Most of the Japanese koi grow from 22 to 26 inches long.

The average weight of a Japanese koi is 12 pounds. But some of them can make it double.

Due to selected breeding and intensive care in the farm from breeding to the adult stage, they grow really fast and big.

Jumbo Koi

Jumbo Koi FishJumbo koi are the largest type of koi. A Jumbo koi grows at least 30 inches long and weighs over 20 pounds.

But larger size jumbo koi grow up to 34 to 36 inches. Weight of these size jumbo koi can be 22 to 26 pounds.

Jumbo koi are bred selectively. Only the selected young koi are taken intensive care to grow this size.

How Big Do Butterfly Koi Get?

Butterfly KoiButterfly koi, longfin koi, or dragon carp can grow as long as 36 to 40 inches in length. But the most common size you will see is 24 inches.

Weight of an adult butterfly koi ranges from 12 to 16 pounds. But some of them can grow up to 20 pounds.

Butterfly koi have longer fins that make them larger. These fins will grow until the blood vessel can’t supply blood to the fin.

Fins and body of butterfly koi grow slowly. Therefore, the older the fish the longer it will be.

To be longer and bigger, you have to supply your butterfly koi adequate amount of quality food. Also, you have to make sure the quality of water and temperature is suitable for its growth.

If you stock aggressive fish with butterfly koi, they can eat the fins. So, make sure you have good mates for them to make them grow big.

What is The Biggest Recorded Koi Fish?

Big Girl KoiBig Girl is the biggest recorded koi fish in history. In 2007 she weighed 90 pounds. She was three times larger than any adult koi back than and now.

Her owner purchased him from a Japanese breeder when she was seventeen years old. At this age, she was 40 inches long. That means it is twice of a normal big size koi. It was reported that she doesn’t grow longer after that.

Since her, no koi fish grow as big as her, not even close to her.

Factors Which Influence The Size and Growth of Koi

Genetics of The Koi

The most important factor that determines the size and growth of a koi is its genetics. Low-quality domestic koi will not grow like Japanese high-quality koi no matter how well the pond is and how good quality food you supply.

Koi fish got their size and beauty after a long time of selective breeding. Koi breeders breed koi selectively and they never disclose their secret of breeding highest quality koi.

After the baby stage, only a few koi are selected for intensive care. This selection process consists of a number of criteria like the head, backbone, and frame.

Size of Pond

Large Koi PondSize of pond plays a huge role in the growth of a koi. You can’t grow a big size koi in a small pond. A koi won’t get big if it doesn’t have enough space to live freely.

That is why commercial koi breeders use large deep pond for their koi. It is recommended that you have at least 3 feet deep pond for koi and a good open water area.

The population of Koi Pond

The population of koi in the pond has a large impact on the growth of it. If you stock too many koi in a small place, they will not grow well.

For every 1 inch of length of koi, it will need 10 gallons of water. So for a 20 inches koi, you will need 200 gallons of water. If you are growing koi commercially, then you should give them more water. The more water they have, the larger they will grow.


Growth of a koi depends on its age. A koi fish grows fast during the first couple of years of its growth stage. The growth rate then becomes slow and after a certain period, it stops.

If a koi fish don’t grow well during its youth stage, it will not get big afterward. Therefore for growing big koi, good care should be taken from birth.

Nutrition, Quality, and Type of food

Koi fish eatingThe growth of a koi fish depends on the food you provide to it. The food should be consists of all the necessary ingredients for growth.

If the koi are feed several times a day, then the digestion and nutrition absorption will be good. hence they will grow quickly. Nutrition is more important in the young stage when the growth rate is high. Therefore, in this stage,

Quality and Temperature of Water

Water quality and the temperature is the most important factor that defines how big a koi will get.

Koi grows best at 65 and 75 F temperature although they can tolerate a wide temperature range. But the too high and too low temperature will definitely affect their growth.

The chemical quality of the pond water should also be maintained. As koi are carp, the Dissolve Oxygen (DO) should be maintained properly. Other chemical measures like pH and Nitrate concentration plays a huge role in koi growth and health.


Environment plays a key role in the growth of koi. Have you ever wondered why only Japanese breeder produces the top quality koi?

It is due to the environment of Japan. The environment, climate, and meteorology of Japan are perfect for koi.

If you visit a koi farm pond in Japan, you will notice a nice and calm environment. There will be hardly anyone to disturb the koi in their final growth pond.

How to Make Your Koi Grow Bigger

If you want to grow your koi bigger, then you can follow the following tips –

  • Keep the population small in your pond so that they get more space to grow.
  • Stock your koi in a large and deep pond.
  • Provide fresh quality food.
  • Make sure the food is balanced with all nutritional ingredients.
  • Feed them at least 6 times a day with regular interval.
  • Make sure there is enough natural food for the koi in your pond.
  • Maintain the ideal water quality and temperature for koi growth.
  • Take good care of your koi in the winter.
  • Make sure they aren’t feared of anything and ensure a good pond environment.
  • Select only the best young koi that have shown good growth.

How long does it take for a koi fish to grow to full size?

Usually, It takes three years for a koi fish to grow to full size. But some koi fish can take ten years to reach its final growth stage.

A koi grow about 4 to 6 inches every year for the first couple of years of its life. Then the growth rate becomes slow. Usually, at the age of 10 to 12 years, they finally stop growing. But some can grow even after that age.

How big do koi fish get in a 10 gallon tank?

A 10 gallon fish tank measure 20″ x 10″ x 12″. Where 20″ is the length and 10″ is the width. The least dimension of your fish tank should be more than twice of your fish length. That means a koi fish can get up to 5 inches in a 10-gallon tank.

But this is a bad idea to stock a 5 inches koi in a 10 gallon tank. Koi fish requires more free space than other fish as they are actually carp. Therefore, you should get a larger tank for your koi fish.

Do koi fish stay small?

Small koi fishNo, koi fish doesn’t stay small. A good quality young koi has an average growth rate of 4 inches per year if it is supplied with proper food and water quality.

However if the koi are stressed during their first stage of growth, they may stay small. There are also some koi species that stay small like the domestic koi.

Does the size of the pond hinder a Koi’s growth?

Yes, the size of the pond has a big effect on the growth of koi. A young domestic koi will live happily in 50 gallon water. But you can’t grow a 36 inches koi in a 1000 gallon pond. A koi of this size needs more water to live freely.

To stock normal koi fish your pond must be at least 3 feet deep. For growing larger koi, you will need an even larger and deeper pond.

If you have ever seen any Japanese koi farm, they have large deep ponds for growing their largest size koi. They also keep the population of koi very low in these ponds. This way the koi’s get the maximum facility to grow.

4 thoughts on “How Big Do Koi Get & How to Make Koi Grow Bigger”

  1. I have 3 x 24 ” koi, unfortunately I am moving and can not have a massive pond ,could you tell me roughly how big my new pond would need to be and how deep. Thank you

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