Aquarium Fish Stocking Calculator
Calculate how many fish your aquarium can safely hold based on tank size, fish species, and filtration.
Stocking Level
Fish stocking determines how many fish your aquarium can safely support. Overstocking leads to poor water quality, stress, disease, and shorter lifespans.
The classic rule of thumb:
1 inch (2.5 cm) of fish per gallon (3.8 L) of water
However, this is a simplified guideline. The real answer depends on fish species, filtration capacity, and tank dimensions.
Better stocking guidelines:
| Fish Size Category | Gallons Per Inch | Liters Per cm |
|---|---|---|
| Small (tetras, guppies) | 1 gal per inch | 1.5 L per cm |
| Medium (angelfish, gouramis) | 2 gal per inch | 3 L per cm |
| Large (oscars, goldfish) | 3-5 gal per inch | 4.5-7.5 L per cm |
| Bottom dwellers (corydoras) | 1 gal per inch | 1.5 L per cm |
Tank surface area matters more than volume. A long, shallow tank supports more fish than a tall, narrow one because oxygen exchange happens at the surface.
Key stocking rules:
- Start with fewer fish and add gradually over weeks.
- Always cycle the tank before adding fish (4-6 weeks).
- Better filtration allows slightly higher stocking, but never double the guideline.
- Live plants help process waste and improve water quality.
Minimum tank sizes by popular species:
- Betta: 5 gallons (19 L)
- Neon tetras (school of 6): 10 gallons (38 L)
- Goldfish (single fancy): 20 gallons (76 L)
- Angelfish (pair): 30 gallons (114 L)
- Oscar (single): 55 gallons (208 L)