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Pond Liner Size Calculator

Enter the pond length, width, depth and overlap to get the liner size.

How it is calculated

The liner has to follow the bottom, climb both sides and still leave a margin on top, so each dimension gets the depth twice and the overlap twice: liner length = length + 2 × depth + 2 × overlap and liner width = width + 2 × depth + 2 × overlap. The liner area is liner length × liner width. All inputs use the same unit, usually metres, and the area comes out in square units of it.

overlap is the extra strip you want on each edge, anchored under stones or soil. If the field is left empty, the tool uses 0.3 (30 cm if you work in metres). Length and width must be above zero, and depth and overlap cannot be negative. The formula treats the pond as a simple box with straight sides, so a pond with sloped sides, shelves or a deep centre needs extra material; the result is a minimum for a rectangular pond, not a design drawing.

Worked example

A pond is 4 m long, 3 m wide and 0.8 m deep, with a 0.3 m overlap on each edge. Liner length = 4 + 2 × 0.8 + 2 × 0.3 = 4 + 1.6 + 0.6 = 6.20 m. Liner width = 3 + 1.6 + 0.6 = 5.20 m. The area is 6.20 × 5.20 = 32.24 square metres. So you would ask for a liner of about 6.2 m by 5.2 m, and in practice choose the next standard size up from that.

Try this example →

Common mistakes

  • Adding the depth once instead of twice. The liner runs down one side and up the other, so depth counts on both ends of each dimension.
  • Forgetting the overlap is counted per edge. The formula adds it twice per dimension, so a 0.3 m overlap adds 0.6 m to the length and to the width.
  • Using the deepest point of a sloped or shelved pond as one flat depth. Real ponds with slopes need more liner than a straight-sided box.
  • Mixing units, such as length in metres and depth in centimetres. All four fields must use the same unit.
  • Ordering exactly the calculated size. Liners are sold in standard sizes and folds at corners use extra material, so round up.

About this calculator

A rectangular pond liner needs to cover more than just the pond's footprint — it has to run down both side walls and across the bottom, plus leave extra material anchored beyond the edge. The standard formula is liner length = pond length + (2 × depth) + (2 × overlap), and the same for width, so a 3m × 2m pond that's 0.6m deep with a 0.3m overlap on each side needs a liner roughly 4.8m × 3.8m.

Landscapers and water-garden hobbyists building a koi pond, wildlife pond, or backyard water feature use this calculation before ordering liner material — EPDM rubber and PVC liners are typically sold by the roll or cut to custom size, and ordering short means an expensive reorder, while overestimating wastes material at a real cost per square metre.

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