About the Pond Liner Size Calculator
This pond liner size calculator tells you how big a flexible liner (EPDM rubber, PVC or RPE) you need for a garden or koi pond. Enter the maximum length, width and depth of the hole and how much liner you want to overlap the edge, and it returns the liner length and width, the area, and a size rounded up to whole feet or half meters for ordering. The same dimensions apply to the protective underlayment that goes beneath the liner.
It is meant for DIY pond builders and anyone checking a quote. Flexible liners stretch down the walls and across the floor, so the sheet must be much larger than the pond surface — a common surprise when people first price a pond.
The standard rule adds twice the maximum depth plus twice the overlap to each surface dimension. It covers rectangular, round and free-form ponds (measure the longest length and widest width), and is generous for ponds with planting shelves. Leave the overlap at 1 ft (or 0.3 m) or more so you can anchor the edge under stone or turf.
How to use the pond liner size calculator
- 1Choose feet or meters.
- 2Measure the pond’s longest length and widest width at the surface.
- 3Measure the deepest point and choose an edge overlap.
- 4Read the liner size and order the rounded size for both liner and underlayment.
Formula and method
A flexible liner has to run down one wall, across the floor and back up the other wall, then lie flat around the edge. For each direction that is the surface dimension plus twice the maximum depth plus twice the edge overlap. Using the maximum depth (rather than the average) makes the sheet big enough for the deepest point, and the slack is taken up in folds and on planting shelves.
Liners are sold in whole feet or half-meter increments, so the exact size is rounded up for ordering. Underlayment — a geotextile fleece that protects against roots and stones — is cut to the same size.
- L, W
- Maximum length and width of the pond
- D
- Maximum depth of the pond
- overlap
- Liner left flat beyond the edge on each side
Worked examples
10 × 8 ft pond, 2 ft deep, 1 ft overlap
Length: 10 + 2 × 2 + 2 × 1 = 16 ft. Width: 8 + 2 × 2 + 2 × 1 = 14 ft. The liner is 224 sq ft; at $1.20 for liner and $0.40 for underlayment per sq ft, materials cost about $358.
Metric pond 3 × 2 m, 0.8 m deep, 0.3 m overlap
Length: 3 + 1.6 + 0.6 = 5.2 m; width: 2 + 1.6 + 0.6 = 4.2 m, or 21.84 m². Rounded up to half meters, order a 5.5 × 4.5 m liner (24.75 m²), costing about 396 at prices of 12 (liner) + 4 (underlayment) per m².
Koi pond 16 × 12 ft, 4 ft deep, 1.5 ft overlap
Length: 16 + 8 + 3 = 27 ft; width: 12 + 8 + 3 = 23 ft. A deep koi pond needs a 621 sq ft liner — more than three times its 192 sq ft surface.
Frequently asked questions
How do I calculate pond liner size?+
Add twice the maximum depth and twice the edge overlap to the pond’s length, and do the same for the width. A 10 × 8 ft pond that is 2 ft deep with a 1 ft overlap needs a 16 × 14 ft liner.
How much overlap should a pond liner have?+
Allow at least 1 ft (about 30 cm) on every side, and 1.5–2 ft if you plan to bury the edge in a trench or under heavy coping stones. Excess can always be trimmed after the pond is filled and settled.
Do I need underlayment under a pond liner?+
Yes, underlayment is strongly recommended. A geotextile fleece cushions the liner against stones and roots and is much cheaper than replacing a punctured liner. Cut it to the same size as the liner.
What is the best pond liner material?+
45-mil EPDM rubber is the most common choice for fish ponds because it is flexible, fish-safe and lasts decades. RPE (reinforced polyethylene) is lighter and stronger for its thickness, while PVC is cheaper but less durable in sunlight.
Do planting shelves change the liner size?+
Not with this method. The liner still follows the walls and floor, and using the maximum depth for the whole pond gives enough material to cover shelves; the extra is taken up in folds.