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Aquarium Volume Calculator
Aquarium Volume Calculator — Exact Gallons from Tank Dimensions
Knowing the exact volume of your aquarium is fundamental for accurate dosing, salinity adjustment, and livestock stocking decisions. The total (gross) volume calculated from external dimensions always overstates actual water volume because glass walls take up space, and your water level sits below the rim. For a standard 60×24×24-inch tank with ⅜-inch glass and a 2-inch headspace, gross volume is 150 gallons but actual water volume is closer to 138 gallons — a 8% difference that adds up when dosing expensive trace elements or treating disease. This calculator subtracts glass thickness on all walls and the water level drop to give you the true water volume. Use the actual water volume for all dosing calculations. For sump-based systems, run this calculator separately for the display tank and sump, then add the two water volumes together.
How to Use This Calculator
1
Measure the external dimensions of your tank in inches (outside edge to outside edge).
2
Enter the glass thickness. Common values: 1/4" (0.25), 3/8" (0.375), 1/2" (0.5). Measure or check the manufacturer spec.
3
Enter water level drop — how far below the rim you keep the water. Typically 1.5–3 inches.
4
Click Calculate. Use the actual water volume for dosing, salinity, and chemical calculations.
5
For systems with a sump, calculate display tank and sump separately, then add both water volumes together.
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Frequently Asked Questions
Why is gross volume different from actual water volume?
Glass walls on all four sides and bottom take space — a 3/8" thick wall on a 60" tank removes 3/4" from both length and width. The water level is typically 1–3 inches below the rim. These deductions combined can reduce usable volume by 5–15% compared to simple L×W×H/231.
Should I include the sump in my tank volume?
Yes. For dosing purposes always use total system volume — display tank plus sump. Measure both separately and add. Most sumps run half-full or less, so measure at the typical operating level.
How do I convert gallons to liters?
Multiply US gallons by 3.78541. The result box already shows both units.
What glass thickness do standard tank sizes use?
20–40 gallon tanks typically use 1/4" glass. 50–100 gallon tanks use 3/8". 100–180 gallons use 1/2". Very large tanks (200+) may use 3/4" or thicker. Always verify with the manufacturer.
