Pond liner size calculator
Enter your pond's dimensions and we'll size the flat liner sheet to buy, using the length + twice the depth + overlap rule. Measure the hole, not the yard, and round up.
Your pond
Use the longest, widest, and deepest points of the finished hole.
The lip you fold over the edge and bury or hide under rock. About 1 to 2 ft each side; more on a soft or sloping bank.
Formula: liner length = pond length + (2 x max depth) + (2 x overlap), same for width. Estimates only; add extra for steep shelves or an irregular shape. Always size up.
The formula the listings hope you skip
A liner is a flat sheet that has to drape down one wall, across the bottom, and up the other wall, with enough left over to anchor at the edge. So the sheet you buy is always bigger than the pond looks: liner length = pond length + (2 × max depth) + (2 × overlap), and the same for width. An 8 × 6 ft pond that is 2 ft deep with a 1.5 ft lip needs a sheet roughly 15 × 13 ft, not 8 × 6. Buy to the pond dimensions and the liner will not reach.
Overlap: the lip you bury
The overlap is the extra material past the water line that you fold over the edge and bury under soil or hide beneath rock. Plan on about 1 to 2 feet per side, and more on a soft or sloping bank where the edge can slump. This lip is also your margin for error: if the pond settles or you raise the water level later, the buried overlap is what keeps water inside the liner instead of wicking out over the top edge.
Round up to a stock size, and match the underlayment
Liners are sold in fixed sheet sizes, so when your number lands between two, take the larger one, a short liner cannot be patched longer. Trim the excess after the pond holds water, never before. And buy underlayment to the same size in the same order: it goes under the liner every time to protect it from roots and sharp stone, and it is far cheaper than the leak it prevents.
What you'll buy at this size
The calculator points at two purchases sold by the sheet: the liner itself and the underlayment beneath it. Buy both to the same dimensions.
Firestone
Firestone PondGard 45 Mil EPDM Liner
Buy the liner at the sheet size the calculator gives you, not the pond size. 45-mil EPDM is the fish-safe default: flexible into odd shapes, forgiving to install, and it outlasts cheaper PVC by years.
Beckett
Beckett Pond Underlayment
Underlayment goes under the liner every time, cut to the same sheet size, so buy it in the same trip. It cushions the liner from roots and sharp stone, which is the single most common cause of a slow leak.
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