How Many Fish Can I Put in My Aquarium?

Last edited - December 8, 2018

Use this calculator to find out how many fish can fit in your aquarium

What the results mean

Many people know of the rule of thumb, "1 inch of fish per gallon of water" when stocking their aquarium. However, this rule gives an extremely rough estimate because it doesn't consider the shape of the aquarium, the size of the fish, or the temperature. Although, this calculator doesn't take the temperature into account either, it is much more accurate in predicting how many fish will happily fit into an aquarium because it relates the amount of fish with water surface area instead of volume.

Relating surface area to amount of fish is more accurate because the amount of surface area determines the rate at which oxygen is dissolved into the water. The more surface area, the more oxygen your fish can get. Temperature also has an effect on the amount of fish your aquarium can hold in that lower temperatures can hold more oxygen. An aquarium at 60F degrees can hold a significant amount of fish compared to an aquarium at 80F degrees. However, don't lower the temperature below a fish's comfort zone just to be able to house more fish.

Additionally, do not rely on this calculator as your only source because it is only an estimate. Before buying your fish, do some research such as how aggressive they are, if they produce a lot of waste, if they are territorial, etc. Some fish are highly aggressive to only their species (male bettas for example) so you can only keep 1 of them per aquarium. Other fishes grow huge when they become adults such as plecos (24+ inches) and pacus (30+ inches).

This calculator gives a much more accurate number for the amount of fish your aquarium can hold because unlike the 1 inch per gallon rule, it takes into account those oddly shaped tanks many betta owners have.