The best size for a koi pond depends on how many fish you plan to keep and how much space you have, but a good starting point is at least 1,000 gallons of water. This size provides enough room for a small group of koi to grow and swim comfortably, while also supporting better water stability and easier maintenance. A larger volume of water helps dilute waste more effectively and reduces the impact of temperature swings.
Ideally, the pond should be at least 3 feet deep to protect the fish from predators and temperature extremes. Koi can grow over two feet long, so planning for their full adult size is important when choosing pond dimensions. If you plan to keep many koi or create a more elaborate ecosystem, a pond in the range of 2,000 to 5,000 gallons offers even more flexibility and better conditions. Building a pond that's too small often leads to overcrowding, water quality problems, and stress for the fish.
