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How Small Can a Koi Pond Be? (Is Bigger Better?)

With the warm, summer weather approaching, perhaps you’ve thought about adding a Koi fishpond to your backyard, outdoor oasis. Starting this task takes time, effort and money on your part, but it’s also a very rewarding and enjoyable pastime once complete. Right now, you may be wondering to yourself, ‘how small can an outdoor fishpond be or is bigger actually better when it comes to a Koi pond?’

The absolute ‘smallest’ size for a Koi pond is 500-gallons and 2 feet deep, and that’s for a mere 2 fish. A 1,000 gallon, 3 feet deep pond is better and will nicely sustain 2 to 4 Koi fish. This species can grow quite large and needs plenty of space to swim about. Therefore, it’s imperative that the pond be big enough otherwise, the fish will not fair well. When it comes to keeping Koi in an outdoor fishpond, bigger is always better!

Now that you know a Koi fishpond should hold at least 500-gallons of water, let’s take a closer look at this in more detail below. We’ll discuss if you can put Koi in a small pond (a 300-gallon size, for example) and if there is such a thing as ‘small’ Koi fish. We’ll also explore the pros and cons of starting a Koi pond, if Koi fish will stay small when kept in a small pond, how many Koi fish can be put in a small pond and whether (or not) they can even survive in anything less than a 500-gallon fishpond.

And now, if you’re ready to learn more about creating and maintaining your own outdoor Koi fishpond, then let’s get to it!

How Deep Should a Small Koi Pond Be?

The absolute minimum recommended depth for a small koi pond is 2 feet.  Anything less is dangerous for the fish. Not only could it potentially suffocate the fish, but it also makes them an easier target for predators. I would say nothing less than a 3-feet deep pond should be considered when creating an outdoor Koi fishpond. The fish will need room to swim should the top few inches of the pond freeze over during the winter months.

Can You Put Koi in a Small Pond?

You can put Koi in a small pond, but it’s not recommended. This species can grow to be quite large (12 to 16 inches is the average length for domestic Koi, but they can get as big as 26 inches for Japanese Koi and a whopping 36 inches for Jumbo Koi). Therefore, the bigger the pond, the better! The minimum size, I’d say, is a 1,000-gallon design with at least 3 feet of depth although, I’ve read some people keep 2 Koi fish in a 500-gallon, 2-feet deep pond.

beautiful koi fish in pond

Can You Get Small Koi?

There really is no such thing as ‘small’ Koi! The smallest ones are around 16 inches full-grown, which is quite big for the average domestic fish. Sunburkins are often referred to as ‘the poor man’s Koi’ and grow to about 15 inches long. They are a happy, active fish that get along with most other species of pond fish. Consider these Koi if making a ‘small’ outdoor fishpond. If healthy and well cared for, they can live up to 20 years!

Will Koi Stay Small in a Small Pond?

Koi will not grow big in a small pond. They need adequate space to move about freely. Keeping this species of fish in a cramped space will negatively affect their overall health. They’ll likely suffer from stress and become physically debilitated while increasing the susceptibility to disease. The only way they ‘stay small’ is if they die young! And, I’m sure you can agree (especially if you’re an avid fish-lover like me) this is not acceptable, under any circumstances.

How Many Koi Fit in a 300-Gallon Pond?

A 300-gallon outdoor pond is not big enough for Koi fish. The general rule-of-thumb is one Koi to every 500 gallons of water. The only time a 300-gallon pond would work is if you’re using it to rear or spawn Koi fry. As they grow, however, they would need to be moved to at least a 500-gallon pond. And, only 2 small Koi fish (at the most) should be in anything less than a 1,000-gallon pond. Typical water conditions when calculated correctly allow for 1 inch of fish per 10 gallons of water, on average.

What is the Best Size Pond for Koi Fish?

The ‘best’ size outdoor pond for Koi fish is at least a 1,000-gallon, 3-feet deep area. When it comes to raising Koi, the bigger, the better! A 3000-gallon outdoor fishpond is ideal for Koi. This will provide enough space for at least 6 fish (3 males and 3 females, preferably) to live a happy, healthy life! The smaller the pond, the greater the risk of losing your fish to disease, stress or predators! When in doubt, always opt for a larger aquatic environment, if possible.

What are the Pros and Cons of Having a Koi Pond?

Just like with any hobby or pastime, there are often pros and cons associated with it. Understanding the benefits and drawbacks will help you decide if it’s indeed something you’re ready and able to pursue. With regards to starting an outdoor Koi pond, some of the advantages and/or disadvantages include (but aren’t limited to) the following:


  • Hardy – Koi are a very resilient fish. They can live in an outdoor pond all winter long, provided the temperature doesn’t drop below freezing and the water quality is good.
  • Long Life – Koi fish can live up to 100 years, if healthy and well cared for. The average lifespan, however, is 20 to 30 years, which is still a lot by fish standards!
  • Fun to Watch– Koi fish are beautiful to watch! They’re brightly colored fins make them pleasing to the eye while their active nature provides for a fun viewing experience.
  • Peaceful Environment – an outdoor Koi pond creates a calming environment in which to enjoy the beauty of nature. It’s the perfect addition to any outdoor, backyard oasis.
  • Property Value – the addition of an outdoor fishpond will add interest and appeal to your yard as well as increase the overall value of your property. This is undoubtably a ‘win-win’ situation!


  • Cost – Koi are very expensive to purchase. On average, one small fish can cost around $15 each whereas others can cost upwards of $100 (even as much as $1000) each!
  • Size – Koi are large fish and require a lot of space. A 1,000-gallon pond (as big as it sounds) will only house a mere 4 averaged-sized Koi!
  • Maintenance – keeping Koi in an outdoor pond requires routine maintenance and special filtration equipment. These can be both expensive and time-consuming to keep up.
  • Climate Control – Koi can survive in an outdoor pond with 6 inches of surface or less and temperature as low as 0 degrees Celsius. Anything more (or colder) is not recommended.
  • Predators – Koi kept outside are in greater danger from predators, such as birds and/or cats. Providing some type of defense-system, like netting or an electrified fence is often required.


To conclude, the absolute ‘smallest’ size for a Koi pond is 500-gallons of water and at least 2 feet deep. A 1,000 gallon, 3-foot deep pond is better, especially if you want to keep more than 2 Koi fish. The reason being that this species can grow to be quite big and needs a lot of space to swim around freely.

A pond that’s too small will negatively affect the overall health and happiness of the fish. The perfect size for 4 to 6 Koi, for example, is a 3000-gallon pond that’s around 6 feet deep. When it comes to a Koi fishpond, bigger is always better!

Hopefully this article has been of help to you. Thanks for reading. Good luck and happy fish keeping!


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