Aquarium Stocking Calculator
The aquarium stocking calculator gives you a realistic, conservative estimate of how many fish your tank can hold. It weighs your water volume against adult fish size and your filtration level to produce a bioload rating, so you can plan a stocking list before you buy livestock.
Treat the result as a guideline, not a hard limit. The old one-inch-of-fish-per-gallon rule ignores adult size, waste output, territory and swimming needs. When you are unsure, understock — a lightly stocked aquarium is more forgiving, more stable and healthier for its inhabitants.
Frequently Asked Questions
How many fish can I put in my aquarium?
There is no single number, but a good rule is to stock conservatively based on adult fish size, not the size at purchase. This calculator rates your bioload from your water volume, the fish you plan to keep and your filtration, so you can see whether a stocking list is light, appropriate or overstocked.
Is the one-inch-per-gallon rule accurate?
Not really. It ignores adult size, body mass, waste output and behavior, and it breaks down badly for larger or messy fish. A single 6 inch fish produces far more waste than six 1 inch fish. Use bioload and adult size instead, and understock when in doubt.
What happens if my aquarium is overstocked?
Overstocking raises ammonia, nitrite and nitrate, stresses fish, spreads disease more easily and demands constant maintenance. If the calculator flags your tank as overstocked, upgrade filtration, increase water changes, rehome fish or move up to a larger tank.
