Aquarium Volume Calculator
Find your fish tank's water volume in gallons and liters from its dimensions.
This is the tank's full geometric volume. Gravel, rocks, decor, and the inch or two of air below the rim mean the real water volume runs roughly 10% lower — shown as the stocking estimate.
How it works
Tank volume is just length times width times height, but the units trip people up. This does the multiplication and converts cleanly into both gallons and liters so you can stock and dose correctly.
The figure it gives is the tank's full geometric volume. In practice, gravel, rocks, decorations, and the gap below the rim mean the actual water volume is a bit lower — often around ten percent less.
Knowing the real number matters for more than curiosity: stocking levels, heater wattage, and medication or fertilizer doses are all worked out per gallon or per liter of water.
Frequently asked questions
How do I calculate aquarium volume?
Multiply length by width by height in the same units, then convert. This tool handles the conversion to US gallons and liters for you.
Why is my actual water volume lower than the tank size?
Substrate, rocks, decorations, and the unfilled space near the top all displace water, so the real volume is typically about 10 percent below the geometric figure.
Why does volume matter for a fish tank?
Stocking guidelines, heater sizing, and dosing of medications or fertilizers are all based on water volume, so an accurate number keeps your fish safe.