Tank Size Calculator
Instantly calculate the volume of rectangular and cylindrical tanks in gallons, litres, and cubic feet. Perfect for aquariums and water storage.
Calculate Your Tank Capacity
Enter your tank’s dimensions and shape to instantly see the total volume in litres, US gallons, UK gallons, and cubic feet.
Volume Estimator
Get precise capacity measurements for your tank or aquarium.
How it Works
Understanding tank volume calculations
Select Shape
Choose whether your tank is a standard rectangular aquarium or a cylindrical storage tank.
Enter Dimensions
Input the length, width, and height (or diameter) using your preferred unit of measurement.
Instant Conversion
We calculate the total cubic volume and instantly convert it to litres, US gallons, and UK gallons.
Real-World Adjustment
We also provide an estimated “actual” water volume, factoring in a standard 10% loss for gravel and decor.
Standard Aquarium Sizes & Dimensions
A general overview of common rectangular aquarium sizes and their typical external dimensions (in inches).
| Tank Size | Typical Dimensions (L × W × H) | Volume (Litres) | Best For |
|---|---|---|---|
| 10 Gallon | 20″ × 10″ × 12″ | ~37.8 L | Betta fish, small nano setups |
| 20 Gallon (High) | 24″ × 12″ × 16″ | ~75.7 L | Small community fish, beginners |
| 29 Gallon | 30″ × 12″ × 18″ | ~110 L | Medium community, planted tanks |
| 55 Gallon | 48″ × 13″ × 21″ | ~208 L | Large community, cichlids |
| 75 Gallon | 48″ × 18″ × 21″ | ~284 L | Large fish, extensive aquascaping |
| 125 Gallon | 72″ × 18″ × 21″ | ~473 L | Advanced hobbyists, large species |
Tank Volume FAQ
Answers to the most frequently asked questions about calculating tank capacity, aquarium setup, and volume displacement.
To calculate the volume of a rectangular tank, multiply the length by the width, and then multiply that result by the height (Length × Width × Height). Ensure all measurements are in the same unit before multiplying, then convert the cubic result to gallons or litres.
A ’20-gallon’ tank is a nominal size. When filled to the absolute brim, it holds exactly 20 US gallons (about 75.7 litres). However, once you add substrate (gravel/sand), decorations, and leave a gap at the top for the lid, the actual water volume is typically around 17 to 18 gallons.
Yes. Substrate, rocks, driftwood, and internal filters displace water. A general rule of thumb is to subtract 10% to 15% from the total calculated geometric volume to estimate the actual amount of water the tank will hold once fully set up.
To convert cubic inches to US gallons, divide the total cubic inches by 231 (since there are exactly 231 cubic inches in one US gallon). For Imperial (UK) gallons, divide the cubic inches by 277.42.