The “1 inch of fish per gallon” rule is the starting point every fishkeeper hears first. It is rough, it ignores bioload and adult size, but it is a fast sanity check before you overstock a new tank. This aquarium stocking calculator applies it.
Aquarium Stocking Calculator
Treat the number as a ceiling, not a target, and always size for the fish’s adult length, not the size it is at the pet store. The aquarium supplies guide covers filtration and heating for the gallon size you land on.
Gunner Vance