For a rectangular tank, multiply length × width × height (all in the same unit). If you used inches, divide by 231 to get US gallons. This calculator does it instantly—just enter your dimensions and choose your preferred unit.

Bow front tanks have a curved front glass that slightly reduces internal volume compared to a rectangular tank of the same outside dimensions. The Bow Front Coefficient (default 0.90) adjusts the rectangular volume formula. A value of 1.0 represents a flat front, while lower values represent a deeper curve. Most manufacturers list the actual water capacity—use the slider to match it for your specific model.

Our calculator uses gross internal volume. Actual fill capacity is often less due to substrate, decorations, equipment, and the water level being below the rim. Manufacturers may quote approximate filled volume. Use the coefficient slider for bow front tanks to fine‑tune the estimate.

This tool is optimized for rectangular and bow front aquariums. For cylindrical tanks, the formula is π × radius² × height. For corner and unusual shapes, separate calculators are recommended. However, you can often approximate a bow front tank’s volume by treating it as a standard rectangle with a coefficient.

Volume in cubic inches = Length × Width × Height.
• US Gallons = cubic inches ÷ 231
• UK Gallons = cubic inches ÷ 277.419
• Liters = cubic inches ÷ 61.0237
If you measure in centimeters, divide cm³ by 1000 for liters or by 3785.41 for US gallons. Our calculator handles all these conversions automatically.

Fresh water weighs approximately 8.34 lbs per US gallon (1 kg per liter at 4°C). The calculator displays the estimated total water weight based on the computed volume. Don't forget to account for the glass, stand, and accessories when placing your tank.

1 US liquid gallon equals 231 cubic inches (≈3.785 liters).
1 UK imperial gallon equals 277.419 cubic inches (≈4.546 liters).
Almost all aquarium products in North America use US gallons. This tool shows both for your convenience.