Aquarium Stocking Calculator
Add your tank size and the fish you're planning, and we'll calculate your true stocking level and filtration load, then flag compatibility problems, tank too small, schooling fish kept in too-small groups, fin-nippers, predators, and temperature/pH mismatches.
Frequently Asked Questions
How does the stocking calculator work?
It compares total bioload (a per-species waste weight) against your tank's capacity, which scales with usable water volume and filter turnover. It also runs species-specific checks for minimum tank size, schooling group size, temperament conflicts, and overlapping temperature and pH ranges.
What stocking percentage should I aim for?
Under ~90% is comfortable for most keepers. Up to 100% is workable with strong filtration and consistent water changes. Over 100% means you should reduce numbers, upgrade tank size, or add filtration.
Why does it warn about schooling fish?
Schooling species like tetras, rasboras, and corydoras become stressed, nippy, and short-lived when kept in groups that are too small. Keep them in their recommended minimum group or more.
Is the 1 inch per gallon rule accurate?
Not really. The old rule ignores body mass (a 3 inch goldfish produces far more waste than three 1 inch tetras), activity level, and filtration. It badly overestimates capacity for chunky or messy fish and underestimates it for small schooling species. A bioload-based calculation like this calculator is far more reliable.
How many fish can I keep in a 10 or 20 gallon tank?
It depends entirely on the species. A 10 gallon comfortably holds one betta plus a snail, or 6 to 8 small tetras. A 20 gallon opens up options like a school of corydoras plus a centerpiece fish. See our stocked example builds for 10 gallon, 20 gallon, 40 gallon, and 55 gallon tanks.
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