Tank Volume Calculator
Use this tool to calculate your aquarium volume in liters, US gallons, and UK gallons. It works best with rectangular tanks.
How to calculate aquarium liters
If your tank is rectangular, volume calculation is straightforward. Measure the internal length, width, and water height, then multiply those values together.
Formula (centimeters)
Liters = (Length × Width × Height) ÷ 1,000
Why divide by 1,000? Because 1 liter equals 1,000 cubic centimeters (cm³).
Formula (inches)
Liters = Length × Width × Height × 0.016387064
This conversion is based on cubic inches to liters. If you prefer gallons, this calculator provides both US and UK gallons automatically.
Gross volume vs net volume
Aquarists often confuse total tank capacity with actual water volume. They are not the same:
- Gross volume: Full geometric capacity if the tank were filled to the top edge.
- Net volume: Real water in the system after accounting for air gap at the top, substrate, rocks, wood, and equipment.
Net volume matters most for dosing fertilizers, water conditioners, medications, and deciding fish stocking levels.
Why accurate liters matter
1) Safer medication dosing
Underdosing can fail to treat disease; overdosing can stress or kill fish and invertebrates. Estimating too loosely is risky.
2) Better filtration planning
A common target is 4× to 8× turnover per hour for many community aquariums. Knowing true liters lets you pick the right filter and flow settings.
3) Smarter stocking decisions
Fish care is about more than “inches per gallon,” but water volume still affects waste dilution, oxygen availability, and long-term stability.
4) Reliable maintenance routines
When you know net water volume, your weekly 20% or 30% water changes become precise rather than approximate.
Example calculation
Suppose your internal tank dimensions are 90 cm × 45 cm × 45 cm:
- Gross liters = (90 × 45 × 45) ÷ 1,000 = 182.25 L
- If filled to 95% and with 10% displacement:
- Net liters = 182.25 × 0.95 × 0.90 = 155.82 L (approx)
That net figure is what you should use for dosing and operating decisions.
Common aquarium size reference
| Tank Dimensions (cm) | Gross Volume (L) | Approx US Gallons |
|---|---|---|
| 60 × 30 × 30 | 54.0 | 14.3 |
| 80 × 35 × 40 | 112.0 | 29.6 |
| 90 × 45 × 45 | 182.3 | 48.1 |
| 120 × 45 × 45 | 243.0 | 64.2 |
| 150 × 50 × 60 | 450.0 | 118.9 |
Practical tips for better accuracy
- Measure internal dimensions with a tape measure, not product label estimates.
- Use actual water height, especially if your tank is intentionally not filled to the rim.
- Adjust for hardscape-heavy layouts (rocks/wood can displace significant volume).
- Recalculate after major rescapes.
- Keep a note of your net liters for maintenance logs and dosing charts.
FAQ
Can I use this for rimless and braced tanks?
Yes. The method works for both. Just measure internal dimensions and your real water line.
What if my aquarium is bowfront or curved?
This calculator is optimized for rectangular tanks. For curved tanks, use manufacturer specs or divide the tank into simpler geometric sections and estimate.
Should I include sump volume?
If you run a sump, add the operating water volume in the sump to your display tank net liters for whole-system dosing.
How much does aquarium water weigh?
Roughly 1 liter of freshwater weighs about 1 kilogram (2.2 lb). Saltwater is slightly heavier. The calculator includes a quick weight estimate.
Final thoughts
Aquarium success is often about consistency, and consistency depends on accurate numbers. Use the calculator above to get a reliable liter estimate, then build your feeding, dosing, filtration, and maintenance plan around that value.