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The Goldfish Sanctuary

proper Goldfish care

How many fish can I keep?

In order to determine how many fish you can safely keep in a container, you must find the surface area of the container you wish to put them in. Don't forget that your goldfish will grow! The following formula works if the top of your tank is rectangular. Be sure to count the goldfish's tail when considering how many inches of fish you have.

Surface Area = Length X Depth
Inches of goldfish = Surface Area / 30

example 1

Let's say your tank is 18 inches long, 10 inches deep, and ten inches high. If we multiply the length (18) by the depth (10) we come up with 180 square inches of surface area. Since we need 30 square inches of surface area for each inch of fish, we can keep 6 inches of fish. So I could keep 6 one-inch fish in this tank. Or I could keep 3 two-inch fish in this tank. Or I could keep 2 three-inch fish. Or any combination that adds up to six inches.

example 2

I have an 18 gallon tank. Length is 24 inches. Depth is 12 inches. Height is 15 inches. The Surface area is 288 square inches (24 X 12). I divide by 30 (and round down) to get nine inches of fish.

If the top of your tank is circular:

Surface Area = (Width of Circle/2) X (Width of Circle/2) X Pi

inches of goldfish = Surface Area / 30

Image Orelup1 is taken from Pete's Pond Page and is used with the permission of the photographer, Pete Orelup.