Fish Tank Calculators

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Aquarium Stocking Calculator

Build a proposed fish list, compare its documented tank requirements with your usable aquarium volume, and see where social or temperature concerns need more planning. This is an estimate, not a guarantee of compatibility or animal welfare.

Build your stocking plan

Use usable water volume when possible.
Volume unit
Or calculate volume from tank dimensions
Substrate, decorations, equipment, and headspace reduce actual water volume.

Fish

How aquarium stocking is calculated

  1. Your aquarium's usable volume is calculated from gallons, liters, or dimensions.
  2. Each selected species contributes its documented minimum tank requirement multiplied by quantity.
  3. The combined requirement is compared with usable aquarium volume.
  4. Schooling, temperament, temperature, and missing-data warnings are checked separately.

Understanding your stocking level

Lightly stocked means substantial unused requirement remains. Moderately stocked is within the model's reasonable range. Heavily stocked leaves little margin. Overstocked means the documented minimum requirements exceed the usable volume.

Why the 1-inch-per-gallon rule is limited

Adult length alone does not describe waste production, swimming space, territory, schooling, filtration, or maintenance. This calculator does not use the 1-inch-per-gallon rule as a universal capacity formula.

Aquarium stocking tips

Use actual water volume, add fish gradually, test ammonia and nitrite, allow margin for maintenance, and check each species' social and temperature requirements before combining fish.

Example: A 20-gallon aquarium with one species requiring a 10-gallon minimum is evaluated differently from a 20-gallon aquarium containing several schooling fish with larger group requirements.

Frequently asked questions

How many fish can I put in my aquarium?

Capacity depends on species, adult size, behavior, group requirements, filtration, and maintenance, not only on gallons.

Is the 1-inch-per-gallon rule accurate?

It is an oversimplification. It ignores species differences, territory, schooling, oxygenation, filtration, and actual water volume.

Can I calculate stocking for multiple fish species?

Yes. Add each species and quantity. The calculator combines documented tank requirements and flags concerns separately.

Does this calculator check compatibility?

It checks available tank-size, schooling, temperament, and temperature context. It does not guarantee compatibility between individual fish.

Should I use actual water volume or tank size?

Use actual usable water volume when possible because substrate, equipment, decorations, and fill level reduce the nominal tank capacity.

Does filtration change stocking capacity?

Filtration and maintenance affect practical stocking, but stronger filtration cannot compensate for an inappropriate tank size or incompatible fish.