That is 144 cubic feet, about 1,077 US gallons. Using the maximum depth instead would overstate it by a third.
How the pond liner calculator works
PondLinerCalc sizes the liner so it reaches the bottom of the deepest point on both sides and still overlaps the edge: liner length = pond length + 2 × maximum depth + 2 × overlap, and the same for the width. It then rounds each side up to the next 5 ft (or 1.5 m), the steps most EPDM and PVC liners are sold in, and suggests underlayment of the same size. Volume is length × width × average depth, multiplied by π/4 for round or oval ponds, at 7.48 US gallons per cubic foot or 1,000 litres per cubic metre. The pump should turn that volume over once an hour, or twice for koi.
Pond liner sizes for common ponds
Rectangular ponds with a 1 ft overlap each side.
| Pond | Depth | Liner needed | Gallons |
|---|---|---|---|
| 6 × 4 ft | 1.5 ft | 11 × 9 ft | 269 |
| 8 × 6 ft | 2 ft | 14 × 12 ft | 718 |
| 10 × 8 ft | 2 ft | 16 × 14 ft | 1,197 |
| 12 × 10 ft | 3 ft | 20 × 18 ft | 2,693 |
| 15 × 10 ft | 3 ft | 23 × 18 ft | 3,366 |
| 20 × 15 ft | 4 ft | 30 × 25 ft | 8,977 |
Frequently asked questions
How many gallons are in a cubic foot?
7.48 US gallons. A cubic metre is 1,000 litres.
How do I find the average depth?
Measure the depth at several points and average them. For sloped sides, about two-thirds of the maximum depth is a good guess.
How else can I measure pond volume?
Note your water meter before and after filling the pond, or time how long a hose takes to fill a bucket.
Is PondLinerCalc free?
Yes, with no sign-up or ads, and your pond details stay in your browser.
Should I buy a bit bigger than calculated?
Yes. Measure the dug hole, not the plan, and round up: a liner that is too small cannot be fixed, while extra can be trimmed.