Fish Tank Stocking Calculator

About this calculator

This calculator finds tank volume from its dimensions and applies the traditional “one inch of fish per gallon” guideline (roughly 1 cm per 2 liters) to suggest a safe total fish length — a rough surface-area-and-bioload heuristic from classic fishkeeping literature, not a precise biological limit.

Beginner aquarium hobbyists use it as a starting point before stocking a new tank, but experienced keepers and fish stores treat it only as a rough guideline: it breaks down for fish with a lot of body mass relative to length (goldfish, large cichlids), for fish that need more swimming room than the rule implies, and it ignores filtration capacity and bioload, which matter more than raw inches for actual water quality.