Aquarium stocking calculator for safer fish planning
Stocking is where many tanks quietly go wrong.
TanksConnected helps you plan fish stocking alongside tank volume, filtration, adult fish size and long-term maintenance.
Common stocking questions this calculator helps with
These are the real fishkeeping questions people usually ask before buying fish or changing a stocking plan.
- How many fish can I have in my tank?
- Is my fish tank overstocked?
- How many fish can go in a 100 litre tank?
- What fish can I keep in my aquarium?
- Can I keep an Oscar in a 240 litre tank?
- Should stocking be based on adult fish size?
Try the basic stocking calculator below without an account. Add a tank volume, search fish from the TanksConnected species database, and get a simple stocking preview.
Create a free account when you want to save tanks, add filters, unlock fuller bioload guidance, log water tests, track water changes and keep your aquarium history.
Basic aquarium stocking preview
Enter your tank size, add fish, and get a simple stocking estimate. This is the quick public version — filters, saved tanks, water tests and full history unlock with a free account.
Search and select a fish first, then choose how many to add. This public calculator uses basic adult size and species data. It does not include your filters, maintenance routine, nitrate trend or saved tank history.
Create a free account to save this tank, add filters, unlock fuller bioload guidance, track water tests, log water changes and build your aquarium history.
Extra stocking guidance, FAQs and related tools
Adult size first
Tiny shop fish can become large, messy adults. Stocking needs to be judged against their grown size.
Waste load matters
A tank can look empty and still be heavily stocked if the fish are large, messy or territorial.
Maintenance proves it
Nitrate rise, water clarity and behaviour all help show whether the stocking level is actually working.
Stocking is more than litres
There is no perfect calculator, but structured planning is far better than guessing. TanksConnected gives fishkeepers a clearer way to think about stocking.
Frequently asked questions
How does an aquarium stocking calculator help?
An aquarium stocking calculator helps you think about tank size, adult fish size, filtration, waste load and maintenance before adding fish. It should be used as guidance, not as permission to overstock a tank.
Should stocking be based on adult fish size?
Yes. Stocking should always consider adult fish size, not the small size fish are sold at in shops. Many common aquarium fish grow much larger and produce far more waste as adults.
Does filtration change how many fish I can keep?
Better filtration can help process waste and improve water movement, but it does not remove the need for swimming space, territory, oxygen and regular water changes.
Can a tank be overstocked even if the water looks clear?
Yes. Clear water does not always mean low waste. Nitrate trends, fish behaviour, aggression, oxygen levels and maintenance demand all help show whether a tank is genuinely coping.