Aquarium Stocking Surface Area
Calculator
Results
- Water surface area (cm²)
- 4,800
- Water surface area (m²)
- 0.48
- Total fish length supported (cm)
- 120
- Number of fish of that size
- 20
Pool and aquarium results
| Water surface area (cm²) | 4,800 |
| Water surface area (m²) | 0.48 |
| Total fish length supported (cm) | 120 |
| Number of fish of that size | 20 |
formula-map diagram
- Water surface area (cm²)
- 4,800
- Water surface area (m²)
- 0.48
- Total fish length supported (cm)
- 120
- Number of fish of that size
- 20
Pool and aquarium relationship
Formula
fish cm = surface area(cm²) ÷ 100 × allowance per 100 cm²= 4800
Note
This is a simplified model: it applies a standard geometric or physical formula to the numbers you entered. Volumes assume a regular shape and an even average depth, and the kidney shape uses the common 0.45 × (A + B) × L area approximation. Chemical doses convert a target change into a product mass using the strength or label dose you enter, because the amount of active ingredient varies from product to product; they ignore pH, temperature, buffering, sunlight, bather load and existing chemical interactions. Heating uses Q = m × c × ΔT with c = 4186 J/kg·K and ignores heat losses to air, ground and evaporation; evaporation and cover figures use the rate you enter, not local weather. Aquarium stocking by surface area is a rule of thumb, not a biological limit. Always follow the product label and test the water before and after dosing, and consult a pool or aquarium professional for anything you are unsure about.
More in Pool and aquarium
See all →Frequently asked questions
Why does this calculator use surface area instead of the old 'one inch of fish per gallon' rule?+
Oxygen enters the water and carbon dioxide leaves it primarily at the water's surface through gas exchange, so a tank's capacity to support fish is fundamentally limited by that surface area, not by total volume. The inch-per-gallon rule ignores tank shape entirely and badly misjudges capacity for tall, narrow tanks versus long, shallow ones of the same volume.
Why can two tanks with the same volume support very different numbers of fish?+
A long, shallow tank has much more surface area exposed to air than a tall, narrow tank holding the identical volume of water, so it supports meaningfully more oxygen exchange and, in turn, more fish. This is exactly the situation the inch-per-gallon rule gets wrong, since it only looks at volume.
What's the actual guideline this calculator uses for stocking density?+
A common rule of thumb is roughly 1 inch (2.5 cm) of adult fish length per 12-30 square inches (75-190 cm²) of surface area, with the lower end for larger or more active fish and the higher end for smaller, calmer ones. This is still an approximation — actual bioload also depends on fish species, waste production, and filtration capacity, not surface area alone.
Does strong aeration or a heavily planted tank change how many fish I can safely keep?+
Yes — an air stone, powerful filter return, or spray bar increases surface agitation and effectively boosts the gas-exchange rate beyond what still water would provide, and healthy, actively photosynthesizing plants also contribute oxygen during daylight hours. Both let a tank support a modestly higher stocking density than a bare surface-area calculation alone would suggest.
Are labyrinth fish like bettas or gouramis an exception to the surface-area method?+
Yes — labyrinth fish have evolved an accessory breathing organ that lets them gulp atmospheric air at the surface, making them considerably less dependent on dissolved oxygen than typical gill-breathing fish. This means the general surface-area stocking guideline is more conservative than strictly necessary for these species, though they still need enough surface access to reach air.