How do I size a pond liner?

Liner length = pond length + 2 × max depth + 2 × overlap, and the same for width. The liner must climb out of the hole on every side.

How much overlap does a pond liner need?

At least 1 foot on every edge so the liner can be secured with edging stones; 2 feet is safer on sloped ground.

What liner thickness should I use?

45 mil EPDM rubber is the standard for koi and garden ponds; 20 mil PVC is cheaper but far less durable.

Pond Liner Calculator

Enter your pond's digging dimensions and get the liner size to order — including the extra needed to climb out of the hole and lock under edging.

Pond length (ft)

Pond width (ft)

Max depth (ft)

Overlap per edge (ft)

Overlap is the extra liner on each edge that gets weighed down with stones or buried — 1 ft per edge is the usual minimum.

How the math works

liner length = pond length + 2 × (max depth + overlap)
liner width = pond width + 2 × (max depth + overlap)

Think of it in cross-section: the liner runs down one wall of the hole, across the bottom, and back up the other side — that's the pond length plus two depths. Then each edge needs extra to spill over the rim and tuck under edging stones, which is the two overlaps. The same logic applies to width. When you order, liners come in set sizes, so always round up to the next available size — you can hide extra liner under rocks, but you can't stretch a short one.

FAQ

My pond is an irregular shape — what dimensions do I use?: Use the maximum length and maximum width of the dug hole, measured at the rim. The formula only needs the longest run in each direction.
Does shelf depth matter?: No — the formula uses the maximum depth. Planting shelves only reduce water volume, not liner size.
What about underlayment?: Buy geotextile underlayment the same size as the liner. It protects against roots and sharp stones — the number one cause of liner punctures.

Pond Liner Calculator

How the math works

FAQ

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