Water Tank Capacity Calculator

How to use

1. Select the tank shape.
2. Enter the inner (internal) dimensions in feet — using the outer size gives a higher estimate.
3. The capacity will be shown in liters, US gallons and UK gallons.

Note: 1 liter of water = 1 kg, so the full tank weight matters when checking the roof strength. Tanks are usually filled to 90–95%, so the actual usable capacity will be slightly less.