How Big Do Koi Fish Get?

Are you considering buying the majestic koi fish for its charm, color, and attractiveness?

Do you want it in your house to help relax and rejuvenate you, and to show off at competitions?

Yes, koi fish are most popularly grown to compete in competitions for their size. It’s the reason why people are willing to even pay in six figures for some breeds koi fish!

As the biggest koi fish is the winner at these competitions, you may wonder how big do koi fish get. You may also wonder which koi fish is the best to buy, and how you can increase its growth.

Well, the answers to them are intriguing, so read on to find out!

How Big Do Koi Fish Get?

Koi fish are one of the largest fish species in the world grown in ponds. A koi fish can easily reach three feet long and weigh 12 pounds in the right environment and a temperature of about seventy-five degrees!

However, this depends on various factors and the type of koi fish you choose to breed.

Different Types of Koi Fish

There are three main types of koi fish, domestic, Japanese, and jumbo.

  • Domestic koi are the US-bred and have the least growth because of their genetics. They usually grow to a maximum of only 12 to 15 inches long.

  • Japanese koi are most famous for their size and color, where they usually grow from 22 to 26 inches long.  While its average weight is 12 pounds, some can grow to double the weight! The secret to their fast and significant growth is the selective breeding and intensive care adopted until their adult stage.

  • Jumbo koi is the largest type, growing to at least 34 to 36 inches long and weighing over 20 pounds. The selective breeding adopted by breeders is how they grow to this size.

How Big Can Butterfly Koi Grow?

The butterfly koi or dragoon crap is another koi variant with large fins. They have an average 24-inch size but can grow up to 36 to 40 inches in length. They weigh between 12 to 16 pounds but may sometimes reach 20 pounds.

The specialty of the fish is its fins, which make them larger.

The fins, however, grow only as long as there blood supply to the fins. Be careful about the fishes you place with them because aggressive fishes can end up eating the fins. 

Other Factors Influencing the Koi Size

Various factors influence the koi’s growth size and speed. They include:

Water temperature

The best temperature for koi fish to grow in is seventy-five degrees Fahrenheit because warmer water promotes faster metabolism. It helps your fish maintain an ideal growth rate, so that the body and muscle mass increases quickly.

That’s why koi tends to grow faster in the warm and consistent temperatures of aquariums, than ponds. Fluctuating or lower temperatures, like in a pond, lead to a slower metabolic rate and growth.

So if you live in the northern hemisphere, be ready for a slower growth rate in winter when the pond freezes!

Water quality

Water quality is also essential because clean and regularly pumped water promotes healthy koi growth Of course, they can live in cloudy or dirty water, but it dramatically affects their growth and vitality.

That’s why it’s better to use aeration kits and healthy bacteria to oxygenate, and ensure your pond and aquarium water remains crystal clear.


Yes, a koi’s growth DOES depend on its diet!

They grow better eating fish food containing fats and carbohydrates, and enhanced with vitamins and proteins. There are also some fish food brands with ingredients that will improve your fish’s color!


Yes, just like humans, the koi genes also affect its size.

Koi fish has the genetic blueprint to grow fast, small, big, or small where gigantic parents produce gigantic offsprings, and vice versa. Similarly, don’t expect low-quality koi to grow into the high-quality Japanese koi; with even the best food and environment!


Koi fish grow better if they have the freedom to move around, without any inhibitions comfortably. Too many fishes in a pond can restrict your fish’s growth.

It leads to reduced space and stunted growth and increases the potential for disease issues, and water pollution. Each inch length of koi needs 10 gallons of water, meaning a 20-inch koi needs 200 gallons of water.

So you can imagine the amount of water you will need if you have more fishes in the pond! Remember, the more water they have, the better and larger koi will grow.


Do you wonder why Japanese breeders produce the best quality koi?

It’s because of the tranquil Japanese environment.

Yes, the surroundings also affect your koi growth. They grow best in calm and peaceful places, where there’s hardly anyone or anything to disturb them.

A large, deep pond

Your koi fish grows best in a large, deep pond because it has enough space to exercise and develop muscles. You cannot expect to grow a big koi fish in a small pond!


The final factor affecting the koi size is its age.

Like any other living organism, koi fishes grow the fastest when young and the slowest when they are older. Their growth rates also practically double in adolescence but decreases as they age.

Most koi fishes stop growing at the age of 10-12 years, but some do develop even after that age.

Looking at all these factors, except for the genes and age, everything else lies in your hands! So you can imagine how big your young koi fish can get with prominent genes, grown somewhere spacious, in clean and aerated water, and fed nutritious food!

How Fast Do Koi Grow?

If you wonder how fast your koi grows, the short answer is about 0.66mm per day or 2cm per month. In other words, the koi will grow about 9 inches in the first year.

They grow about 15-16 inches by age two and usually reach full size in three years. However, some koi fishes take ten years to reach its maximum growth potential!

How to Increase the Koi Growth Rate

With most of the factors governing a koi’s size lying in your hand, the following tips can help you increase their growth rate:

  • Make sure there’s enough space for them to swim around freely without any overcrowding.
  • Feed your fish more of high-protein foods, but avoid feeding too many carbohydrates. AND, don’t end up overfeeding your koi!

Remember, koi fish don’t have any stomachs. So any excess food passes through their gut partially digested. It’s better to provide them a little food, about six times a day at regular intervals.

  • Buy young koi fish. This way, you have better control over its growth, and with the right conditions, it can help it grow well. Older fish have a shorter time to grow, and as mentioned earlier, they grow slower as they age. So a younger fish offers better prospects of developing the biggest.
  • Last but not least, maintain an ideal water temperature of 75-82 degrees F for optimal koi fish growth. And remember, your koi fish will need extra care in winter.

General FAQ About Koi Fish

How fast do koi fish grow?

They grow about an inch a month, and about 9 inches in the first year.

How can I increase my koi’s growth rate?

It’s quickly done by maintaining the ideal temperature, ensuring they have enough space in the pond, and feeding them high-quality food.

What makes koi grow faster or slower?

Various factors determine how fast or slow your koi grows. They include water quality, temperature, space, genetics, and food.

What is the biggest recorded koi fish?

It was in 2007 that the largest koi fish was recorded in history. Big Girl weighed 90 pounds, about thrice the weight of any adult koi then and now! She didn’t grow much after that, and no koi fish has since then grown as big as her.

Final Thoughts

Well, now you know enough about how big do koi fish get, and how to breed them to their maximum potential. You also know what the best breed is, and the right diet to grow them to the pride of any competition!

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