Aquarium Volume Calculator
Find a rectangular aquarium's water volume.
Find how much water a rectangular fish tank holds.
How the Math Works
The Aquarium Volume Calculator uses the fundamental geometric formula for rectangular prism volume: gallons = L × W × H ÷ 231. Here, L (length), W (width), and H (height) are measured in inches, representing the aquarium's three dimensions. Multiplying these together gives the volume in cubic inches. The division by 231 converts cubic inches to gallons because 1 gallon equals 231 cubic inches - this conversion factor bridges the gap between the metric-derived cubic measurement and the imperial volume unit commonly used for liquid containers.
Practical Applications
To use this calculator practically, first measure your rectangular aquarium from side to side for length, front to back for width, and from bottom to top for height, ensuring all measurements are in inches. Input these three values into the calculator or apply the formula manually: multiply length times width times height, then divide the result by 231. For example, an aquarium that is 24 inches long, 12 inches wide, and 16 inches tall would equal 24 × 12 × 16 = 4,608 cubic inches, divided by 231 equals approximately 20 gallons. Always measure to the actual glass thickness and consider that the water level may sit slightly below the rim.
Day-to-Day Use
Knowing your aquarium's exact volume is essential for responsible fish keeping and proper maintenance. This calculation helps you determine how much water to change during weekly maintenance, select appropriate amounts of water conditioner, and calculate correct dosing for medications or supplements. It also guides you in choosing the right size filtration system, as filters are rated by gallons per hour they can process. Additionally, understanding the volume prevents overstocking fish, helps estimate electricity costs for heating and lighting, and ensures you purchase the correct size replacement tubing, heaters, and other accessories for your aquatic setup.
Worked example
36×18×18 in → ~50.5 gallons.
FAQ
Actual water?
Subtract a little for gravel, décor and the gap below the rim.