How it works
The formula
liner length = pond length + 2 × deepest depth + overlap
liner width = pond width + 2 × deepest depth + overlap
gallons = length × width × average depth × 7.48
liner width = pond width + 2 × deepest depth + overlap
gallons = length × width × average depth × 7.48
- The liner has to go down one side, across the bottom and up the other, so each way it needs the pond's size plus twice the depth. Aquascape, which makes EPDM pond liner, adds 2 ft of overlap for the edging stones, and rounds up to the next stock size.
- Measure the length and width at the widest points, including shelves and curves; an odd shape takes the same liner as the rectangle around it.
- Underlayment goes under the liner to protect it from roots and stones: buy the same size.
- Gallons use the average depth over the rectangle, so a curved or shelved pond holds a little less.
Worked example
Aquascape's example: 8 × 12 ft pond, 4.5 ft deep
- 8 + 4.5 + 4.5 + 2 = 19 ft wide
- 12 + 4.5 + 4.5 + 2 = 23 ft long
- Round up to the next stock liner: Aquascape picks 20 × 25 ft
Liner size by pond size
| Pond | Deepest | Liner | Gallons |
|---|---|---|---|
| 6 × 4 ft | 1.5 ft | 11 × 9 ft | 180 |
| 8 × 6 ft | 2 ft | 14 × 12 ft | 539 |
| 10 × 8 ft | 2 ft | 16 × 14 ft | 898 |
| 12 × 8 ft | 2 ft | 18 × 14 ft | 1,077 |
| 15 × 10 ft | 2.5 ft | 22 × 17 ft | 2,244 |
| 20 × 15 ft | 3 ft | 28 × 23 ft | 4,488 |
Questions people ask
How do I measure for a pond liner?
Take the longest length, the widest width and the deepest point, then add twice the depth and about 2 ft of overlap to each. The overlap tucks under the edging stones.
Should I buy a bigger liner?
A little bigger is fine, and liners come in stock sizes anyway; trim the extra after the pond is filled and edged. A liner that's short can't be fixed without seams.
Does a pond liner need underlayment?
Yes. A felt or geotextile underlayment under the liner keeps stones and roots from puncturing it. Buy the same size as the liner.