Pond Liner Calculator: Sheet Size and Volume

How to use the pond liner calculator

1. Enter the maximum length and width of the pond, at the top of the bank.
2. Enter the maximum depth from the top of the bank to the deepest point, not the water line and not an average depth.
3. Enter overlap. The default is 2 feet total (about 1 foot per side), the overlap DLM Plastics adds to each dimension. Larger ponds with an anchor trench need more.

If you need to bring in dirt to build up the pond edge or a berm, the fill dirt calculator sizes imported fill (not the spoil dug out of the hole). This is a sheet-size check, not an excavation design.

Liner size formula

Liner length = pond length + 2 × depth + overlap, and liner width = pond width + 2 × depth + overlap. Volume for a rectangular planning estimate is length × width × depth × 7.48052 gallons per cubic foot.

A worked example: 20×15×4 ft pond

DLM Plastics uses this example: a 20 × 15 ft pond, 4 ft deep, with 2 ft of overlap needs a liner of 20 + 8 + 2 = 30 ft by 15 + 8 + 2 = 25 ft, a 30 × 25 ft sheet. The rectangular volume is 20 × 15 × 4 × 7.48052 ≈ 8,977 gallons.

Sources & assumptions

How this calculator gets its numbers. Full method: our methodology.

• Liner length = pond length + 2 × depth + overlap; liner width = pond width + 2 × depth + overlap. Default overlap is 2 ft total (about 1 ft per side), the overlap DLM Plastics adds to each dimension.
• Volume is a rectangular planning estimate, L × W × depth × 7.48052 gal/cu ft, not a survey of irregular shelves.
• Use maximum depth from the top of the bank, not average depth or water-line depth.

Sources

1. DLM Plastics, How to Measure for a Pond Liner. States liner width = pond width + depth + depth + overlap (2 feet), and the same for length. Worked example: 20 × 15 × 4 ft pond → 30 × 25 ft liner.

Last reviewed November 12, 2026. A site measurement that follows the pond contours, or the liner manufacturer’s size chart, wins.