How Many Koi Can You Have in Your Koi Pond?

Beautiful koi fish swimming in a clean pond

How Many Koi Can You Have in Your Koi Pond?

Koi ponds are a beautiful natural feature in a backyard or lobby area, but there are limits to how many koi can live in one confined space. Today, we will share the rules that every koi pond owner should follow to maintain a healthy ecosystem for their fish.

Consequences of Overstocking your Pond

It is imperative to avoid overstocking your koi pond because it can lead to problems that will impact the well-being of your fish. They need sufficient space to swim around, and the more fish there are, the more cramped and stressed they will feel, making them more susceptible to diseases.

Too many fish in your koi pond also leads to decreased oxygen levels and waste buildup, which encourages algae growth. When this occurs, it takes a toll on your filtration system. When these problems continue, you must call on professional pond service technicians.

Rule of Thumb for Koi and Goldfish

A minimum of 250 gallons is required for every koi. Even if you start with baby koi, they will continue to grow, so 250 gallons of water accounts for that growth. If you have reproductively mature fish, the minimum gallon amount for every female koi has to double. These fish need a lot of space, so ensure your pond has the minimum capacity to accommodate the number of koi you want.

Use this formula to calculate how much water your pond holds: (L x W x 80%) x average pond depth x 7.48 = total gallons of water in a pond. Only include the 80% if you have a round pond because that part of the formula does not apply to rectangular ponds.

If you are not keen on math, refer to the table below to get an idea of how many koi or goldfish you can have in your pond. Note that this table applies to rounded ponds with an average depth of two feet. You cannot have the maximum number of goldfish plus koi in the same pond, but you can have a handful of each fish if you so choose.

Pond Size (in feet) Max # of Koi Max # of Goldfish
5 X 5 4 7
5 X 8 7 12
8 X 10 13 21
10 X 10 16 25
12 X 10 19 30

How to Prevent Overcrowding

Now that you can make the calculations, the first step to preventing overcrowding in your koi pond is to stick to those numbers, plus a little extra space for any newcomers. Once your koi begin reproducing, you will have to find new homes for the babies before they get too big. Ask your friends, family, and neighbors as soon as possible to find a new owner or call pet stores to see if they accept secondhand koi.


When given the proper nutrients and space to thrive, domestic koi can grow up to fifteen inches long, and Japanese koi can get up to 26 inches long. Purchase filters and aerators that can accommodate a pond a little bit bigger than yours to ensure the pond stays clean. No matter what, it is crucial to have regular koi pond service to ensure the health of your fish and their home. Call Aquatic Gardens whenever you need koi pond help. Our service area covers all of Los Angeles County, and we are glad to be able to serve the local community.