TOOL 04
Stocking
Calculator.
Estimate how many fish your aquarium can hold. This is a rough reference — actual limits depend on filtration, species temperament, and maintenance habits.
Stocking recommendations vary depending on filtration, fish species, tank conditions, and your maintenance routine. Schooling fish should be kept in groups of 6+. Always research species-specific needs before purchasing.
ABOUT THIS TOOL
Stocking
Calculator.
The Stocking Calculator estimates how many fish your aquarium can safely hold, based on tank volume, fish species, and filtration level. It uses a modified version of the 'centimetre per litre' rule, which estimates how much water volume each centimetre of adult fish requires, then adjusts the result based on your filtration capacity.
This tool deliberately provides a range rather than a single number, because safe stocking depends on many factors beyond volume — fish temperament, territory needs, swimming behaviour, and your maintenance routine all matter. A school of neon tetras has very different space requirements from a single territorial cichlid, even at the same body length.
The calculator also respects minimum school sizes for schooling species. For example, neon tetras should never be kept in groups smaller than six, regardless of what the volume calculation suggests. The minimum count shown will never drop below the species' school requirement. Use the result as a starting point for research, not as a shopping list.
HOW TO USE
Using the
Stocking Calculator.
- Enter your tank volumeInput the actual water volume of your aquarium in litres. Use the Tank Volume Calculator if you're unsure of your real capacity — not the manufacturer's stated size.
- Select your fish speciesChoose the species you plan to keep from the dropdown. The tool includes common community species with their adult sizes and space requirements pre-loaded. If your species isn't listed, pick the closest similar one in adult size and temperament.
- Choose filtration levelBasic: sponge filter or single HOB. Moderate: canister filter or upgraded HOB. Heavy: over-filtered with canister plus additional filtration. Your filtration level adjusts the stocking estimate up or down.
- Read the recommended rangeThe primary result shows a minimum–maximum range. The minimum respects the species' school size requirement. The maximum assumes good maintenance and adequate filtration.
- Check the adult size and ruleThe tool displays the expected adult size of your chosen species and the stocking rule applied (e.g. '1 cm per 2 L'). This helps you understand the calculation behind the number.
- Research before buyingThis is a rough reference, not a guarantee. Always research your specific species' temperament, territory needs, compatibility, and swimming space requirements before making purchase decisions. Some fish need more horizontal space; others need vertical territory.
FAQ
Common
Questions.
Is the stocking calculator accurate?
It provides a reasonable estimate based on the 'centimetre per litre' rule, adjusted for filtration. However, no stocking calculator can account for every variable — fish temperament, territory needs, water parameter stability, and maintenance habits all affect what your tank can hold. Use the result as a starting point, not a final answer, and always research your specific species.
Why does the rule say '1 cm per 2 L' — isn't it '1 cm per 1 L'?
The old '1 cm of fish per 1 litre of water' rule is outdated and often leads to overstocking. Modern guidance suggests 1 cm per 2–5 litres depending on species. Slender, schooling fish (like tetras) need less space per centimetre than deep-bodied or territorial fish (like cichlids). Our calculator uses species-specific ratios for better accuracy.
What if I have multiple species in one tank?
Run the calculator for each species separately, then check that the combined total is reasonable. A good approach: calculate each species' maximum, add them up, and ensure the total doesn't exceed what a single-species calculation would suggest for your tank volume. Also research species compatibility — some fish shouldn't be housed together regardless of space.
Why does filtration level affect stocking?
Your filter processes fish waste (ammonia) into less harmful compounds. A more powerful filter processes more waste, supporting more fish. However, filtration alone doesn't solve all problems — overstocked tanks still need more maintenance, and fish need swimming space and territory beyond just clean water. Don't use heavy filtration as an excuse to overstock.
My species isn't listed — what should I do?
Pick the closest similar species in terms of adult size and body shape. For example, if you have ember tetras (not listed), use neon tetra as a proxy — both are small, slender, schooling fish. If you have a species with very different needs (e.g. territorial cichlids), research specific stocking guidance for that species rather than relying on a general calculator.
Should I stock to the maximum number?
No. Stocking to the absolute maximum leaves no margin for error — temperature fluctuations, missed water changes, or a dead fish going unnoticed can tip an overstocked tank into a water quality crisis. Aim for 70–80% of the maximum recommendation. This gives you a buffer and makes maintenance more manageable.