Aquarium Volume Calculator
Calculate the true water capacity of your aquarium tank from its exterior or interior dimensions. Converts length, width, and height into US gallons and liters, and computes the total water weight to ensure your floor and aquarium stand can safely support the load.
Horizontal front length of the aquarium (e.g. 36" for standard 40-gallon breeder)
Front-to-back depth measurement (e.g. 18")
Vertical height of the glass tank (e.g. 16")
Aquarium profile shape
Liquid capacity in standard US liquid gallons
How to Use This Calculator
- Measure the length, width, and height of your tank in inches.
- Select your aquarium shape (rectangular, bowfront, or cylinder).
- View the total gallon capacity and liters.
- Examine the water weight and gross floor load to confirm your stand strength.
Formula & Calculation Methodology
One US liquid gallon equals exactly 231 cubic inches. Freshwater weighs 8.34 pounds per gallon (1.0 kg per liter). Total floor loading requires adding the weight of thick glass panels and gravel substrate.
Worked Example
Standard 40-Gallon Breeder: 36" L × 18" W × 16" H
Standard 10-Gallon Tank: 20" L × 10" W × 12" H
Frequently Asked Questions
Why does my tank hold less water than the manufacturer advertised rating?↓
Manufacturers measure the outside dimensions of the glass frame. Substrate (gravel or sand), internal filters, hardscape driftwood/rocks, and leaving 1–2 inches of air space at the top typically reduce actual water capacity by 10% to 15%.
How heavy is a 55-gallon aquarium when completely filled?↓
A 55-gallon tank contains approximately 460 pounds of water. When combined with the heavy glass tank (~80 lbs) and 60 lbs of substrate, the total filled assembly weighs over 600 pounds (270 kg).
Does saltwater weigh more than freshwater?↓
Yes. Marine saltwater has a specific gravity of ~1.025 and weighs approximately 8.55 pounds per gallon, about 2.5% heavier than freshwater.
What is a limitation when sizing heaters or medication?↓
Always dose medication and size water conditioners based on true net water volume (after subtracting gravel and displacement) rather than empty gross tank dimensions to avoid toxic overdosing.