Aquarium Volume Calculator - Tank Gallons & Liters
Calculate rectangular aquarium volume in gallons or liters from tank dimensions, with estimated water weight.
Volume
19.95 gal
75.5 liters
Estimated Water Weight
166.4 lb
How to Calculate Aquarium Volume
For a standard rectangular tank, volume is simply Length × Width × Height. This calculator converts that raw volume into gallons or liters, the units used to size filters, heaters, and stocking levels, and estimates the water's weight using the standard figures of 8.34 lb per US gallon (about 1 kg per liter).
Example
A standard 24" × 12" × 16" tank has a volume of 24 × 12 × 16 = 4,608 cubic inches, which is 4,608 ÷ 231 ≈ 19.95 gallons — close to the commonly advertised "20-gallon" tank size — and weighs roughly 166 lb of water alone.
Common Use Cases
- Sizing a filter or heater rated for a specific gallon or liter capacity.
- Calculating stocking limits, which are often expressed per gallon of water.
- Checking whether a stand or floor can support the combined weight of tank, water, and substrate.
- Verifying a manufacturer's advertised tank size against its actual dimensions.
FAQs
Why is my calculated volume different from the tank's advertised size?
Advertised sizes (like "20 gallon") are usually rounded to standard industry sizes and don't account for glass thickness reducing interior dimensions, so the calculated volume from exact measurements is often a close but not identical match.
Should I use the full volume when calculating stocking levels?
No — substrate, decorations, and equipment displace some water, so the actual water volume is typically 5-10% less than the tank's full geometric volume. Many aquarists use the full volume as a conservative estimate for filtration sizing.
Does this work for bowfront or cylindrical tanks?
This calculator is designed for standard rectangular tanks. Curved or cylindrical tanks require different volume formulas (based on a cylinder or a more complex curved-front shape) and will show a higher volume than the simple length × width × height calculation for the same footprint.