Input Parameters
Results History (for CSV and PDF export)
After each calculation, copy or note values into this table for exporting multiple scenarios.
| Scenario | Shape | Dimensions | Substrate depth | Decor displacement (%) | Net volume (L) | Net volume (US gal) |
|---|---|---|---|---|---|---|
| No scenarios recorded yet. Perform a calculation to populate this table. | ||||||
Example Data Table
This example demonstrates typical aquarium setups and their approximate net water volumes.
| Tank description | Shape | Dimensions | Substrate depth | Decor displacement (%) | Approx. net volume (L) |
|---|---|---|---|---|---|
| 90 cm planted community tank | Rectangular | L=90 cm, W=40 cm, H=45 cm | 6 cm | 12% | 120 L |
| 60 cm nano aquascape | Rectangular | L=60 cm, W=30 cm, H=36 cm | 5 cm | 18% | 45 L |
| Cylindrical display column | Cylindrical | D=40 cm, H=60 cm | 4 cm | 10% | 65 L |
Formula Used
Rectangular tank volume
For rectangular or cuboid tanks, the gross water volume at the fill height is calculated as:
Gross volume (cm³) = Length × Width × Fill height
Cylindrical tank volume
For cylindrical tanks, the cross–sectional area is circular, so:
Gross volume (cm³) = π × (Diameter ÷ 2)² × Fill height
Substrate volume
Substrate is assumed to form a uniform layer at the bottom:
Substrate volume (cm³) = Base area × Substrate depth
Usable water volume above substrate
Usable volume (cm³) = Gross volume − Substrate volume
Decoration and equipment displacement
Decorations and internal equipment occupy part of the water space, approximated as a percentage:
Decor displacement (cm³) = Usable volume × (Decor percentage ÷ 100)
Net water volume
Net water volume (cm³) = Usable volume − Decor displacement
Unit conversions
- 1 cm³ = 0.001 liters
- 1 liter ≈ 0.264172 US gallons
- 1 inch = 2.54 cm (for imperial inputs)
How to Use This Calculator
- Select the tank shape: rectangular or cylindrical.
- Choose your preferred unit system, either metric or imperial.
- Enter the internal dimensions of your aquarium, using internal glass measurements.
- Specify the actual water fill height, or leave blank to assume full height.
- Provide the average substrate depth, considering gravel, sand, or aquarium soil.
- Estimate the percentage of volume taken by rocks, decor, and internal equipment.
- Click “Calculate Net Water Volume” to see gross, usable, and final net water volumes.
- Transfer interesting scenarios into the results table, then export them as CSV or PDF.
Aquarium Water Displacement in Real Setups
Display Volume Versus Net Water Volume
Tank labels usually show a theoretical display volume measured from external dimensions. Once you subtract glass thickness, air gap at the top, substrate, and decorations, the true water volume can be dramatically lower than the advertised capacity on the box.
Why Accurate Volume Matters for Stocking
Stocking guidelines, such as centimeters of fish per liter, assume a realistic water volume. Overestimating capacity leads to poor water quality, chronic stress, and disease. Using this calculator helps match bioload, filtration, and maintenance routines to actual water volume.
Influence of Substrate Type and Depth
Fine sands, deep aquasoils, and layered substrates displace more water than shallow gravel beds. The tool models substrate as a uniform layer, highlighting how a high-energy planted layout with steep slopes can significantly reduce available swimming space and total circulation volume.
Impact of Hardscape and Internal Equipment
Large pieces of driftwood, rock structures, background walls, and internal filters remove water volume. Estimating them as a percentage keeps the interface simple. For heavily scaped tanks, entering higher displacement percentages gives a more realistic working capacity.
Tuning Filtration and Heating Capacity
Filter turnover rates and heater wattage recommendations depend on water volume, not glass size. By knowing net liters, you can size equipment correctly, improving thermal stability, oxygenation, and mechanical filtration efficiency while avoiding unnecessary energy consumption.
Planning Water Changes and Dosing
Fertilizer dosing, medications, and remineralization salts are usually specified per liter. Accurate net volume prevents underdosing and dangerous overdosing. The calculator gives a solid reference when preparing water-change buckets, drip systems, or automatic dosing schedules for planted and reef aquariums.
Comparing Different Tank Shapes and Layouts
Rectangular and cylindrical tanks with similar external volumes can hold different water amounts. Tall designs lose more volume to substrate and decor. By quickly comparing scenarios with this tool, aquarists can optimize layout aesthetics without sacrificing essential swimming space and system stability.
Frequently Asked Questions
Is this calculator suitable for irregularly shaped tanks?
The calculator is optimized for standard rectangular and cylindrical aquariums. For bow-front or custom shapes, you can still use it by approximating the main dimensions, but results should be treated as estimates rather than perfectly precise volumes.
Should I include external filters in the displacement percentage?
External canister filters do not reduce tank water volume because they add additional water volume in hoses and the canister body. The displacement percentage should cover only internal equipment, like internal filters, skimmers, heaters, and air-driven sponge filters.
What decor percentage should I use for a typical aquascape?
Lightly decorated community tanks might use five to ten percent. Heavy hardscape aquascapes with large rocks and wood can reach twenty percent or more. Start conservatively, then adjust the percentage after visually judging how much water space remains.
Can I use this tool for marine or reef aquariums?
Yes. The displacement principles are the same for freshwater, brackish, and marine systems. Reef tanks often contain dense live rock, so using a higher decor displacement percentage gives a more realistic estimate of net water volume for dosing and filtration.
Why does my heater size depend on net water volume?
Heaters are rated according to how much water they can warm by a certain temperature difference. If net volume is smaller than expected, an oversized heater may cycle aggressively. Using accurate net volume helps select a stable, efficient heater rating.
How often should I recalculate displacement for my aquarium?
Recalculate whenever you significantly change the layout, such as adding large rocks, new driftwood, deepening substrate, or removing major decor pieces. For stable long-term scapes, checking the values once or twice per year is usually enough.