Fish Tank Stocking Calculator
Calculate how many fish your aquarium can safely hold based on tank size and fish sizes.
Uses the inch-per-gallon rule with adjustments.
Maximum Fish Count
Fish tank stocking uses the classic “inch per gallon” rule as a starting point, with adjustments for fish size and tank type.
Basic rule:
Maximum fish inches = Tank Volume (gallons) × 1 inch per gallon
Maximum fish count = Maximum fish inches / Average fish size (inches)
When using liters, the calculator converts to gallons (1 gallon = 3.785 liters).
Adjustments:
- Small fish (under 2"): The rule works well — you can stock close to 1 inch per gallon
- Medium fish (2–4"): Reduce to 0.75 inches per gallon (larger fish produce more waste)
- Large fish (4–8"): Reduce to 0.5 inches per gallon
- Very large fish (8"+): Individual research needed; rule does not apply
Important factors beyond the rule:
- Filtration capacity (aim for 4–10× tank volume per hour)
- Surface area matters more than volume for oxygen exchange
- Territorial fish need more space per individual
- Live plants improve stocking capacity by 10–20%
Common fish sizes: Neon tetra 1.5", Guppy 2", Platy 2.5", Molly 3–4", Angelfish 6", Goldfish 6–8"