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Pond Liner Size Calculator

Work out the liner dimensions for a garden or koi pond: the length and width plus twice the depth and an overlap around the edge — and the nearest stock liner size, underlayment and water volume.

Pond
ft
ft
ft
Liner
ft
Liner left flat around the rim to anchor under stones — commonly 1–2 ft.
$/ sq ft

Results

Liner size needed16 × 14 ftNearest stock size 15 × 20 ft
Liner area224 sq ft
Underlayment224 sq ft
Approx. water volume898 gal
Length
10 + 2 × 2 deep + 2 × 1 overlap = 16 ft
Width
8 + 2 × 2 deep + 2 × 1 overlap = 14 ft
Stock liner area
300 sq ft
Volume assumption
75% of length × width × depth (sloped sides / plant shelves)

Measure the longest and widest points of an irregular pond, and use the deepest point for depth. Plant shelves do not change the liner size, because the liner must still reach the deepest point.

Water volume is approximate; use it for sizing pumps and filters, then confirm with a flow meter or the fill-up time.

How it works

  1. Measure the pond’s longest length, widest width and deepest point.
  2. Choose how much liner to leave around the edge for anchoring.
  3. Pick the shape that best matches the pond for the water volume estimate.
  4. Read the liner size, the nearest stock size and the underlayment area.

Formula

Liner length = pond length + 2 × max depth + 2 × overlap
Liner width = pond width + 2 × max depth + 2 × overlap
Gallons ≈ length × width × depth × shape factor × 7.48

The liner has to run down one side, across the bottom and up the other side, so each dimension gains twice the maximum depth, plus the overlap at both rims. Water volume uses 7.48 gallons per cubic foot and a shape factor of 90% for straight sides, 75% for sloped sides or shelves and 60% for natural shapes. Stock sizes are rounded up to 5 ft steps.

Example

A 14 × 10 ft koi pond that is 3 ft at the deepest point, with plant shelves, a 1.5 ft overlap and 45-mil EPDM at $1.10 per square foot.

Inputs

Pond length (longest)
14 ft
Pond width (widest)
10 ft
Maximum depth
3 ft
Edge overlap each side
1.5 ft
Pond shape
Sloped / shelves
Liner price (optional)
$1.1 / sq ft

Result

Liner size needed23 × 19 ftNearest stock size 20 × 25 ft
Liner area437 sq ft
Underlayment437 sq ft
Approx. water volume2,356 gal
Load this example into the calculator →

Choosing and fitting a liner

Flexible EPDM rubber (commonly 45 mil) and reinforced polyethylene liners are the usual choices for garden ponds. Buy one piece if at all possible — seams are the most common source of leaks — and lay an underlayment of the same area to protect it from stones and roots.

Fold the liner neatly at the corners rather than cutting it, fill the pond partway to settle the liner before trimming, and leave the full overlap until the edging is in place.

Frequently asked questions

What size liner do I need for a 10 × 8 × 2 ft pond?

With a 1 ft overlap: (10 + 4 + 2) × (8 + 4 + 2) = 16 × 14 ft, so a 15 × 20 ft stock liner, or a 14 × 16 ft custom cut.

How much overlap should a pond liner have?

Most builders leave 1–2 ft around the rim so the liner can be anchored under rocks or edging.

Do plant shelves need a bigger liner?

No. The liner is sized from the maximum depth; shelves are part of that envelope.

How many gallons is my pond?

Roughly length × width × average depth × 7.48. The calculator applies a shape factor to the maximum depth to estimate the average.