Calculate the capacity of a rectangular or cylindrical water tank in litres and US gallons.
How to Use the Water Tank Calculator
Select the "Tank Shape" (rectangular or cylindrical) and your preferred "Unit" (feet or metres).
Enter the tank dimensions - length/width/height for a rectangular tank, or diameter/height for a cylindrical tank.
Click "Calculate" to see the tank capacity in litres and US gallons.
Frequently Asked Questions
For rectangular tanks, Capacity = Length × Width × Height. For cylindrical tanks, Capacity = π × Radius² × Height. The result is then converted to litres (and US gallons).
Yes, choose your preferred unit — the calculator automatically converts feet to metres internally before computing the volume.
No, it calculates the full internal geometric capacity assuming the tank is completely full to the given height. Actual usable capacity may be slightly less due to wall thickness, sediment settling, or safety margins.
Yes, it's completely free and requires no sign-up.