Aquarium Volume Calculator (Feet to Gallons)
Use this tool to calculate your aquarium's volume in U.S. gallons by entering the tank’s dimensions in feet. Works for all standard rectangular tanks.
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How to Convert Aquarium Dimensions to U.S. Gallons
Fish tank volumes are typically measured in gallons in the United States. If your tank’s dimensions are in feet, you can easily calculate its total volume using a simple formula. This calculator automates the math and gives you accurate results instantly.
Formula for Converting Feet to Gallons
First, calculate the tank's volume in cubic feet:
Volume (ft³) = Length × Width × Height
Then, convert cubic feet to gallons:
1 cubic foot = 7.48052 U.S. gallons
So:
Volume (gallons) = L × W × H × 7.48052
Example Calculations
- 1 × 1 × 1 ft = 7.48 gallons
- 2.5 × 1.5 × 1.5 ft = approx. 42.2 gallons
- 6 × 2 × 2 ft = approx. 179.5 gallons
Why Knowing Gallons Is Important
- Water conditioners and medications are dosed per gallon
- Filter and heater sizing depends on tank gallons
- Helps determine fish stocking levels
Standard Aquarium Sizes (Feet & Gallons)
| Dimensions (ft) | Volume (Gallons) | Description |
|---|---|---|
| 1 × 1 × 1 | 7.5 | Small cube/nano |
| 2 × 1 × 1.5 | 22.4 | Small community tank |
| 3 × 1.5 × 1.5 | 50.6 | Mid-size planted tank |
| 4 × 1.5 × 2 | 89.8 | Large show tank |
| 6 × 2 × 2 | 179.5 | Predator or reef system |
Displacement and True Water Volume
These calculations assume a completely full tank with no displacement. However, most aquariums contain:
- Substrate (gravel, sand)
- Decorations and rocks
- Filters and internal equipment
These items can displace 5–15% of the water volume. For medication or treatment dosing, use actual measured volume or subtract an estimated margin.
Tips for Accurate Measurement
- Measure interior dimensions for best results
- Don’t include frame or trim in your measurement
- Leave 1–2 inches off the top to avoid overflow
FAQ: Volume Conversions
Can I use this for round tanks?
Only if you convert the shape into an equivalent rectangular prism. For cylinders, use:
π × radius² × height (ft³), then multiply by 7.48.
Is U.S. gallon the same as Imperial gallon?
No. 1 U.S. gallon = 3.785 L, but 1 Imperial gallon = 4.546 L. This calculator uses U.S. gallons only.
Can I convert gallons to liters?
Yes. Just multiply your gallon result by 3.785 to get liters.
What if my tank isn’t a perfect rectangle?
Estimate the average dimensions. For bowfront tanks, average the front and back lengths before multiplying by width and height.
Conclusion
Gallons are the standard unit of volume for American aquarists. Whether you’re setting up a new tank or calculating how much medication to dose, knowing the accurate volume of your tank in U.S. gallons is essential. With this calculator, you can convert any tank dimensions in feet into gallons easily, quickly, and accurately.