Building a backyard pond
The fetched OmniCalculator pond tool combines three jobs in one place: pond size, pond volume, and pond liner sizing. That is especially practical when you are planning a fish pond or garden pond and need the excavation, liner, and fill-water quantities together.
As the source explains, a pond should generally be at least around 2 ft deep if you want to keep fish. The overlap allowance matters too, because the liner has to run down the wall, across the bottom, back up the opposite side, and still leave enough material to anchor at the edge.
How much pond liner do you need?
Omni's pond liner method uses the pond length, width, depth, and overlap width. The same dimensions also work for the underlayment, since it sits directly beneath the liner.
Liner length = length + 2 × (depth + overlap)
Liner width = width + 2 × (depth + overlap)
Liner area = liner length × liner width
How to calculate pond volume
The water volume is simply the pond plan area multiplied by the pond depth:
For a rectangular pond, the area is length × width. For a round pond, the area is π × d² / 4. Once you have cubic feet, converting to gallons or liters is straightforward.