Water Tank Capacity Calculator
Calculate water tank capacity in liters and gallons from tank dimensions.
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How to use
- Select the tank shape.
- Enter the inner (internal) dimensions in feet — using the outer size gives a higher estimate.
- 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.
Frequently Asked Questions (FAQ)
Which tank shapes are supported?
Rectangular or cuboid tanks and cylindrical tanks, with dimensions entered in feet.
What results does it show?
Volume in cubic feet, capacity in litres, US and UK gallons, and the approximate weight of the full tank in kilograms.
Should I enter the outer or the inner dimensions?
Enter the inner, or internal, dimensions in feet. Using the outer size gives a higher estimate than the tank really holds.
Should I fill the tank to the full calculated capacity?
Tanks are usually filled to 90 to 95 percent, so the usable capacity is slightly less than the calculated value.