Want the short answer to how fast Koi grow? Under ideal conditions, the average Koi will grow to between 6 and 8 inches by the end of its first year, and by the age of three, it will have achieved full adult size.

Koi fish are attractive freshwater ornamental fish commonly kept in decorative ponds.

They were initially cared for by rice farmers in early nineteenth-century Japan and are essentially colorful variants of ordinary carp, but they are far from common! In Japanese, the word “Koi” literally means “love” or “affection.”

If you’re thinking about getting a Koi or have just acquired one and want to know how fast they grow, you’ve come to the correct spot. We discuss the sizes you may expect and other relevant facts, like variables that can impact your Koi’s growth.

Koi growth development

A typical Koi may grow between 24 and 36 inches long, while some ‘giant’ types can grow up to 52 inches long. However, impressive sizes are only possible if the pond conditions are ideal and the pond is large enough. In any event, growing your Koi to develop to these enormous sizes will be a difficult feat.

There are various aspects to consider regarding the size of the fish, especially if you are seeking to breed the larger species of Koi carp.

These are some examples:

Genetics of Koi

The genetics of the Koi play a big influence in deciding how large the fish will be. If a particular Koi does not contain the specified qualities, it will simply not develop into a gigantic specimen – regardless of how excellent the pond environment may be.

Some Koi will reach a size of 20 inches if cared for properly and kept in an appropriate habitat due to genetic predispositions. For example, domestic Koi in an aquarium may only grow 12 to 15 inches long; however, traditional Japanese Koi can grow 26 inches long.

Under ideal conditions, the average Koi will grow to between 6 and 8 inches by the end of its first year, and by the age of three, it will have achieved full adult size.

How fast do Koi grow? Growth chart for Koi fish

This chart is based on the typical Koi’s growth rate; therefore, not every fish will be the same size you see here. This is only an essential guide to what you may expect as your Koi grows.

AgeKoi Fish Size
1 month1.1 inches
6 months5.1 inches
12 months9.2 inches
18 months12.6 inches
2 years15.6 inches
2.5 years18 inches
3 years20.1 inches
3.5 years21.6 inches
4 years23.4 inches
4.5 years24.6 inches
5 years25.7 inches
5.5 years26.6 inches
6 years27.3 inches
6.5 years28 inches
7 years28.5 inches

How fast do baby koi grow?

Do you want to know how quickly your baby koi will grow? The baby koi’s growth rate is around 0.66mm every day, or nearly an inch (2 cm) per month, equating to approximately 9 inches over the first year.

1–6 weeks

A newborn Koi grows approximately.03 inches (.071 cm) every day until it is 6 months old. So, by Week 1, your Koi will be about.20 inches (.5 cm), and by Week 6, it might grow 1.2 inches (3 cm).

The baby Koi may be brown at this age, or it may be the orange or red that we see in adults, but the colors will not be as vibrant as they will be as it grows. They might be white, yellow, black, or gray as well.

2–6 months

By 2 months, the young Koi will be around 1.6 inches (4 cm) long; by 6 months, the Koi might grow up to 5.1 inches long (13 cm).

At this point, the Koi’s color should continue to grow. You may notice that the color changes, deepens, and becomes more visible.

7–11 months

When the Koi reaches 6 months, its growth rate slows to 0.2 inches (.06 cm) every day until it enters its second year. The Koi will be around 5.8 inches (15 cm) long by the seventh month and will continue to develop at a similar rate.

As the Koi matures, its colors will shift, becoming brighter and more profound.

One year

How big should a 1-year-old koi be? By the time your Koi is a year old, it might reach 9.2 inches (23 cm), although it could be smaller or larger depending on the species and your Koi’s surroundings.

In its second year, the plant is growing at a rate of about.21 inches (0.5 cm) daily.

Two years

Your Koi will be around 15.6 inches when it reaches its second year (40 cm). The daily growth rate will continue to drop as it ages.

The color of the Koi is usually at its optimum by its second year.

Three years

Some Koi are already adult-sized, measuring between 15 and 16 inches, while others might grow to be 20 inches or larger by age three. This is because a Koi takes around three years to evolve into a fully mature adult.

How to Keep Your Koi Fish From Stunting

White and Orange Koi Fish

There are a few things that might slow down your Koi’s growth. Stunted Koi fish live longer, which is interesting, but it is up to the fish keeper whether they want to intentionally slow their Koi’s growth or make their fish as comfortable as possible during its life.

Stunting is usually caused by stress or disease, which might develop under the following circumstances.

Tank Dimensions or Pond Size

The basic guideline is that each adult Koi needs at least 250 gallons of water. If you have a female capable of spawning, you’ll need 500 gallons of water for each female.

However, larger is always better.

However, it is strongly advised that you should not limit Koi to a tank and instead provide them with a habitat in a pond. The pond should be at least 1,000 gallons in capacity and three feet deep.


An overloaded tank will almost certainly limit the growth of your Koi. For example, if your pond is just 1,000 gallons, you should only have three or four medium-sized Koi or two huge Koi in total. The more Koi in a small place, the worse the water quality will be, and your Koi will grow anxious.


What is the best water temperature for Koi Fish? The temperature should be between 60°F and 75°F. While Koi can tolerate temperatures below and above this range, the water quality can degrade outside their ideal temperature range.


A well-balanced food can help a Koi flourish. You should keep the food properly and discard any leftovers 6 months after opening, regardless of the date on the packaging. You should invest in protein-rich pellets that are also abundant in vitamins and minerals.

How much you feed your Koi will undoubtedly influence its development rate.

Water quality

  • The ideal pH range is between 7.0 and 8.5.
  • Ammonia levels should be 0 (you don’t want to observe levels greater than 0.25; any higher, and your Koi’s life is jeopardized).
  • Nitrate levels should range between 20 and 60 ppm.
  • Nitrites can be less than 0.25 ppm but should be fewer than 0.

The oxygen levels in your pond or aquarium may be lower than what the Koi require. This is because the oxygen level in the water will rise when the water is changed.

How often should I change the water in my aquarium/pond?

Every week, change at least 10% of the water. If changing the water every week is not practical, then change around 25% of the water every 2-4 weeks. In addition, the overall amount of water should alter twice a year.

Flow in the Koi pond or aquarium is vital because it encourages them to exercise.

Increase the flow of water throughout their active period. It will help them flourish in the long run.

Read more about Koi pond maintenance.

How Big Do the Most Common Koi Fish Varieties Grow?

From above of multicolored koi fishes with bright spots swimming in clear transparent water of pond in reserve of tropical country

The most popular koi fish varieties are the fast-growing western-bred domestic Koi, which are cheap to buy as juveniles, the butterfly koi with its dragon-like form, and the highly sought-after Japanese Koi.

Domestic Koi Fish

The domestic Koi will develop to an average length of 12 to 15 inches thanks to a genetic composition that predetermines one of the quickest growth rates among all koi kinds.

Because of their diminutive size, koi fish are low-maintenance alternatives for fishkeepers who don’t have the space to build up a pond and want to maintain their Koi in an aquarium.

The many color patterns on these koi fish make them a magnificent addition to any aquarist’s collection without requiring a significant initial investment. In addition, domestic Koi are significantly less costly than Koi imported from Japan.

Japanese Koi

Traditional Japanese Koi grow larger than most domestic Koi, reaching lengths of 22 to 26 inches. These koi fish will also outlive domestic species, surviving an average of 25 to 35 years.

Because of its extraordinary longevity, Japanese Koi are a pet fish that will need a dedication to maintaining healthy and well-cared for, even if it occasionally outlives its initial owner.

Japanese Koi are rarely happy in an indoor aquarium since they are accustomed to broad open swimming spaces and ponds at least 3 feet deep, suitable for hibernating during the winter months.

Butterfly Koi Fish

Butterfly koi, sometimes known as dragon carps, reach an average length of 24 inches, with some reaching 36 inches.

Because of their long, flowing fins, they might appear larger than they are. There’s a reason they’re called longfin koi! Their fins develop much slower than they do. Thus a koi’s fins may become more complicated and impressive as they age.

The fins of a butterfly koi will grow as long as the blood vessels that give them oxygen and nutrients do.

Their beautiful yet sensitive fins render them prone to fin rot. On the other hand, butterfly koi may regenerate their fins and tails if treated in time.

Owners of butterfly koi will usually maintain them as a single species in an aquarium or pond or will avoid keeping them alongside fin nippers.

Jumbo Koi Fish

Jumbo koi variations may grow to be 34 to 36 inches long (or 48 inches in the case of Big Girl).

The typical weight of a jumbo-sized koi is from 22 to 26 pounds.

Because they require specialized fish food to grow to these gigantic sizes, jumbo koi breeders and owners will devote far more time and resources to their koi collection than a domestic koi owner.

Given that giant koi fish are produced from massive parents, even as youngsters, it is advised that they be housed in adequately large outdoor ponds that are suited for their adult size.

Close Up Photo of Koi fish

How do you make Koi grow faster?

You may encourage your Koi to develop quickly by providing them with a big, warm environment and a high-quality feed.

  • As a beginner, go for a bigger breed.
  • Select the females.
  • Provide them with balanced meals that include a variety of proteins, carbs, and fats.
  • Avoid overcrowding your pond or tank.
  • Keep the water quality and temperature stable.
  • Take precautions throughout the winter.
  • Make your pond bigger.
  • Maintain a stress-free or stress-controlled environment for them.
  • Increase the flow of water.
  • Replace the water more regularly.
  • Feed them at least five times every day.
  • Having plenty of natural food in the pond
  • Use a clay supplement to enhance the quality of your water.

However, regardless of how well you care for them, their family trees may restrict their development pace and size. While kids continue to develop for the whole of their life, most of their growth happens when they are young.

How frequently should I feed my Koi?

Experts recommend consuming 3% of a Koi’s daily weight in food, divided between five meals.

Koi can consume various human foods, including lettuce, orange, cabbage, sweet peas, cheerios, shrimp, and others. Aside from that, Koi will assist you by eating the algae. They are, however, not the most common algae feeders.

Is it possible to overfeed Koi?

Yes, Koi may get overfed. Overfeeding is harmful to fish. It might make you sick. As a result, offer the appropriate amount based on the age and breed of your fish.

However, death from overfeeding is not a common occurrence.


If you’re a first-time koi fish owner, the complexities of coaxing them to develop quicker may appear daunting. But, in truth, they are one of the simplest freshwater fish to care for in their size group.

If you’re concerned about your Koi’s development rate, you now have a list of factors/tank conditions to optimize, and you’ll soon have an impressively-sized koi swimming in your tank.

Consistent water quality, growth-focused food, adequate room, and low-stress levels can help your pet koi dragon thrive.