How Big Do Koi Fish Get? (How Fast Do They Grow?}

Are you worried about the tank size of koi fish? How big do koi fish get?

Is your koi fish already showing a tendency of overgrowing its tank or pond? Do you think the tank or pond will become too small for your koi?

This article provides details on the size and growth pattern of koi fish.

How Big Do Koi Fish Get?

A koi fish could grow to about 39 inches (100 centimeters) in length. Different koi varieties have different:

  • body shapes
  • colors
  • speed of growth
  • maximum size they can reach

If you have a domestic koi, you should expect a maximum growth of about 12 to 15 inches. Most domestic koi do not exceed that size in ponds. Japanese koi fish usually grow larger than domestic koi.

They can grow to about 22 to 26 inches in length if fed the right food and in the right proportion.

how big do koi fish get

How Fast Do They Grow?

Koi fish are one of the fastest-growing fish kept in an aquarium or pond. On average, a koi will add 2 centimeters (0.79 inches) in length per month.

  • Your koi fish will add 20 centimeters in 10 months if fed adequately.

Under the right water, tank, and food conditions, your koi fish will be about 6 to 8 inches in length by the end of the year. The koi fish will already be at its adult stage when it reaches about three years.

If you feed your koi fish well and provide adequate conditions and requirements, your koi fish will experience a fast growth rate.

How Big Do Koi Fish Get in a Pond?

Koi fish can have varying sizes, depending on the type of koi you are keeping. It also depends on how you feed them and how well you provide them with their requirements.

Water quality can also affect your Japanese koi’s growth, so you have to make sure you provide the appropriate condition for their growth.

The jumbo-sized koi fish is the giant species of koi fish. They can grow up to 34 to 36 inches long when fed well and kept in appropriate condition.

These pond koi fish are also very colorful, giving your pond a large majestic beautification, moving through the water/.

YouTube video

How Big Do Koi Fish Get in an Aquarium?

Koi fish can grow to a large size regardless of being kept in an aquarium or pond. The only thing is your aquarium will not be able to contain them when they grow too big.

  • The ideal size of a koi fish for your aquarium should be about 12 to 15 inches.
  • There are several other types of koi fish that can grow to about 22 to 26 inches.
  • Other larger types will reach about 34 to 36 inches in size.

These types of koi fish will not be able to fit into your aquarium unless you will be getting an extra-large tank.

The large types of fish will not move freely as the tank will be too small for the koi fish.

The best kind of koi fish for your aquarium is:

  • the standard domestic koi.
  • they will only grow to about 10 to 12 inches

You have to feed them with nutrient-rich foods to make sure they reach their maximum size. Koi fish are social, and one fish has graceful swimming movements. They are also very colorful and make your aquarium a sight to see.

How Fast Do Koi Fish Grow in a Pond?

Before koi fish reach their maturity, they can grow and add about 5 inches in length per year. The growth rate of each koi fish can vary, with some lesser than 5 inches a year, while others can be more.

As they attain maturity, their growth rates slow down as they begin to develop larger girth.

Koi fish tend to grow fast and reach their greatest length within their third to fourth year. Their bodies will also bulk up as they gain length. Some factors can hinder the growth of koi fish, and you have to avoid them.

4 Factors That Hinder Growth of Koi Fish

Here are four factors that can hinder the growth of the fish:

  1. Overcrowding
  2. Poor nutrition
  3. Water quality and condition
  4. Stress

1. Overcrowding

Overcrowding is one of the factors that affect the growth of fish. When overcrowded, koi fish will feel restless and will also reduce the amount of food they consume. You have to avoid overcrowding your pond to prevent a deprived growth of your koi.

2. Poor nutrition

Poor nutrition is one of the greatest factors that hinder your koi fish’s growth. You have to make sure you feed them the right food to avoid poor nutrition. You also have to make sure you feed the fish at the right time and right proportion for your koi’s proper growth.

3. Water quality and condition

Water quality can also cause your fish to experience reduced growth. When the water in the pond becomes dirty or inappropriate for your fish, it can cause them to reduce the amount of food they consume. It can also cause health defects, which will later affect their growth.

4. Stress

Stress is also a factor that affects the growth of koi fish. Koi fish can get stressed due to several reasons causing their immune system to weaken. A weakened immune system causes them to be susceptible to sickness, which will affect their growth.

How Fast Do Koi Grow in an Aquarium?

If properly cared for in an aquarium, koi fish will reach:

  • about 20 inches in length.

Under the right conditions and environment, koi fish will reach:

  • about 6 to 8 inches by the end of their first year.

Koi fish can add about two centimeters per month, making them one of the fastest-growing pond fish.

  • They will also reach their greatest length within 3 to 4 years.

Koi fish will grow as fast as they can in your aquarium if you provide them with everything they need. You also have to avoid overcrowding the tank to prevent them from having deprived growth.

How Big is the Biggest Koi Fish?

Most aquarists know koi fish to be large colorful fish with fast-growing abilities.

They can grow from a small size of 10 inches to a whopping size of 39 inches, but a koi fish named Big Girl broke the record in 2007. The big girl attained a massive length of about 4 feet, which is equivalent to 48 inches.

The 1.2 meters long koi fish weighed about 40 kilograms. Other breeds of koi fish can attain this size only if you provide them with adequate requirements.

YouTube video

Frequently Asked Questions:

1. Do Koi Grow to the Size of Their Tank?

Koi fish do not grow to their tank’s size, but their tank can affect their growth. Koi fish will grow as nature intends for them, but a small tank can hinder their growth.

If you put them in a large tank, they will grow as much as they get well fed and well provided for.

2. How Old is a 5 Inch Koi?

A 5-inch koi fish should be about a year old. On average, koi fish will add roughly 2 centimeters per month and about 5 to 6 inches per year. At best chances and luck, the 5 inches koi should be about eight months.

3. How Big Do Butterfly Koi Get?

Butterfly koi fish is a bit different from the regular koi in terms of sizes. Butterfly koi can grow to about 36 to 40 inches in length when provided with adequate conditions. With food and care, these koi fish will attain their maximum size.

Final Thought

Koi fish have varying growth sizes ranging from domestic koi with about 10 to 12 inches to the large types of about 36 to 40 inches. You have to provide your koi fish with what they need to attain their maximum height.


Thanks for visiting for this article. Check out our home page and search bar with hundreds of aquatic or marine life articles to choose from. Bye for now!


Hello, I'm Jason. I'm the guy behind I volunteer at my local fish shop and I created this site to offer tips and advice on the fish I care for.