Why there is no fish-per-litre answer
Adult body mass, swimming length, social groups, territory, oxygen and waste all scale differently. This calculator reports explicit constraints instead of converting volume into one fish count.
Plan the adult aquarium
Choose full social groups, use internal dimensions and assess every pair. A juvenile that fits today can still make the adult plan unsuitable.
How to use this result
Enter the internal water dimensions or planning values you can verify. Treat the result as a starting estimate, then compare it with the aquarium, equipment and livestock manufacturer’s documentation where relevant.
Assumptions and rounding
Metric values are calculated first and displayed to a practical precision. Advertised tank volume can exceed real water volume because glass thickness, substrate, hardscape and the air gap displace water.
Worked planning example
For an 80 × 35 × 40 cm internal rectangular space, gross volume is 112 litres before displacement. A realistic water volume may be lower, so equipment sizing and water-change preparation should preserve a sensible margin.
Limitations
Shape approximations, pump head, room temperature, lid design and the density of natural materials all affect real-world results. No equipment calculation overrides the care needs in an inhabitant profile.