Free aquarium stocking calculator. Calculate how many fish your tank can safely hold based on surface area and oxygen solubility for healthy fishkeeping.
Overstocking is one of the leading causes of aquarium failure, leading to rapid ammonia spikes, oxygen depletion, and chronic stress-related diseases. However, "stocking" is not just about the number of fish; it involves a complex balance of surface area for gas exchange, biological filtration capacity, and the behavioral needs of different species. This tool provides a nuanced approach to determining the sustainable population for your specific aquarium environment.
Moving beyond the outdated "inch per gallon" rule, our calculator prioritizes the "Surface Area Rule," which recognizes that oxygen exchange primarily occurs at the water-air interface. It calculates the available surface area based on your tank dimensions and estimates the bioload based on the adult size and messiness of your intended fish species. We provide a safety limit that ensures even if a power outage occurs or a filter slows down, there is enough residual oxygen to sustain the inhabitants for a period of time.
Enter your tank's length and width to calculate appropriate fish counts based on surface area. Results are given for small fish (~2.5 cm) and medium fish (~5 cm).
This calculator provides basic guidelines. Actual capacity depends on filtration capacity, fish behavior, and whether plants are present.
Quarantine new fish for 2–4 weeks before adding them to your main tank. Overcrowding degrades water quality rapidly and spreads disease easily.
A common rule is 1 inch of fish per gallon of water. However, this varies by species. Some fish need more space, others less. Research your specific fish's requirements for accurate stocking.
Surface area determines oxygen exchange. Shallow tanks with large surface area can support more fish than tall, narrow tanks of the same volume. Aeration and filtration also affect oxygen levels.
This calculator uses surface area guidelines. Actual stocking depends on fish species, behavior, and tank maintenance. For precise recommendations, consult an aquarium specialist.
Overstocking leads to poor water quality, stress, and disease. Start with fewer fish and add gradually. Monitor water parameters. If ammonia or nitrite rises, reduce stocking or increase filtration.
Acclimate new fish slowly to prevent shock. Float the bag in the tank for 15-20 minutes, then gradually add tank water to the bag. After 30 minutes, gently release the fish. Avoid sudden water parameter changes.