Fish Tank Size Calculator

A fish tank size calculator determines the minimum aquarium volume needed for a given number and size of fish. The classic "one inch of fish per gallon" rule is a starting point, but fish bioload, behaviour, and water filtration capacity all matter significantly.

1. 1Apply the inches-per-gallon guideline: each inch of adult fish body length needs 1 gallon
2. 2Adjust for fish type: schooling fish need extra swimming space; territorial fish need more room per fish
3. 3Small fish (< 5cm): ~2 gallons each | Medium fish: ~5 gallons | Large fish: ~10 gallons
4. 4Always round up and choose a larger tank — bigger tanks are easier to maintain stable chemistry