Fish Stocking / Pond Capacity Calculator

Compute Pond Loads
Select One Pond Surface Area
square feet
Pond Volume
Inches of Fish

The number of fish that can live comfortably in an outdoor pond depends on the size of the fish, species, and size of the pond. The most common rules of thumb for fish load give the number of inches of adult-sized fish per gallon and per square foot of surface area.

The two rules do not take into account other limiting factors (shade, sun, climate, filtration, plants, etc.) and they do not always give the same answer, but they do provide a rough guide for figuring pond loads.

Each rule is described below, or you can use the convenient calculator on the left. If you need to find the number of gallons in your pond or the water surface area in square feet, use these calculators:

Pond Volume

Pond Surface Area

Method 1: Inches of Fish Per Gallon

One rule of thumb for outdoor pond loads is to allot 33.33 gallons per inch of koi, and 20 gallons per inch of goldfish. For example, if you have a school of goldfish and their total length from mouth to tail is 94 inches, then you need a pond that holds at least 20x94 = 1880 gallons.

If you have several koi and their total length is 84 inches, then you need 33.33x84 = 2800 gallons. Koi require more water per inch because they produce more waste.

Method 2: Inches of Fish Per Square Foot

Another rule of thumb for fish stocking is to allot 2 square feet of surface area per inch of fish. For example, if your fish have a total length of 124 inches, then your pond needs a surface area of at least 2x124 = 248 square feet.

Estimates derived from both methods apply only to larger varieties of outdoor pond fish, not smaller fish measuring less than 12 inches long. The smaller the fish, the less water it requires per inch of length.

For instance, suppose one pond has 3 koi that are each 20 inches long, and another pond has 5 koi that are each 12 inches long. Even though the total length of koi is the same in both cases (60 inches), the first pond needs to be larger.

Keep in mind that as your fish grow in size, they will need more water. To keep the population healthy over the years, you must either expand the pond or sell the extra fish. Some species can live comfortably in indoor aquariums if your pond size is limited.

© Had2Know 2010