Pond Liner Calculator
What size pond liner and underlay you need from the pond's length, width and depth plus an edge overlap, with the most it can hold.
A flexible pond liner has to cover the bottom, run up every side and lap over the edge, so each dimension is the pond's length or width plus twice its depth plus an overlap at both edges. A 3 × 2 m pond 0.6 m deep with 300 mm of overlap needs a liner 4.8 × 3.8 m (18.2 m²); a 10 × 6 ft pond 2 ft deep with 12 in of overlap needs 16 × 12 ft. Measure the pond at its longest, widest and deepest points, even if it's curved or has shelves, because the liner folds into the shape. The same size of underlay goes underneath to protect the liner from stones and roots.
- Liner size
- 4.8 m × 3.8 m
- Liner area
- 18.24 m²
- Up to
- 3,600 L
length × width
also the underlay needed
with vertical sides
How it was worked out
- Length: 3 m + 2 × 0.6 m deep + 2 × 300 mm overlap = 4.8 m
- Width: 2 m + 2 × 0.6 m + 2 × 300 mm = 3.8 m
- Liner area: 4.8 m × 3.8 m = 18.24 m²
- If the sides were vertical the pond would hold 3,600 litres; sloping sides and shelves hold less
Measure the hole at its longest, widest and deepest points, even for curved or shelved ponds: the liner folds into the shape. Liners are sold in set sizes, so round up to the next one.
Common use cases
- Order a liner for a new garden or wildlife pond
- Replace a leaking liner
- Check that a pre-cut liner is big enough
- Estimate how much water a pond could hold
How to use
- Choose your units.
- Enter the pond's longest length, widest width and deepest point.
- Enter the overlap you want at each edge (often 300 mm or 12 in).
- Read the liner size and area, and buy the next size up.
FAQ
What size pond liner do I need?
Length = pond length + 2 × depth + 2 × overlap; width = pond width + 2 × depth + 2 × overlap. For a 3 × 2 m pond 0.6 m deep with 300 mm overlaps, 4.8 × 3.8 m.
How much overlap should a pond liner have?
Enough to bury or hold under edging stones all round, commonly about 300 mm (12 in) on each edge. More is easier to work with than less.
Do I need underlay?
Yes, under almost any flexible liner. It stops stones, roots and sharp objects puncturing the liner, and it's the same size as the liner.
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Results are estimates for planning and buying materials, worked out from the figures you enter and typical values (weights, coverage, sizes) that vary by product and supplier. They are not engineering, building or professional advice. Check your local building code, the product maker's instructions and your supplier's figures before you buy or build, and use a qualified professional for structural, electrical and gas work.