Aquarium Stocking Calculator
Rough number of small fish a tank can hold using the inch-per-gallon rule.
liters
cm
How it works
The old rule allows one inch of adult fish per US gallon of water, so the fish count = gallons ÷ adult length in inches. It only suits slim fish under about 3 inches (7.5 cm). Bulky or messy fish such as goldfish, cichlids, and plecos need far more water per inch, and some species need a group or a large swim space. Treat the result as a ceiling, not a target, and research each species. Example: A 200 liter tank with 5 cm fish suggests up to 26 fish.
FAQ
Is this calculator free?
Yes. No signup is needed and nothing you enter is stored.
Is the result exact?
Results are rounded for display. For financial, medical, or legal decisions, confirm with a professional.
Do my numbers leave my device?
No. The calculation runs in your browser.