Pond Liner Calculator
Size a flexible pond liner the right way: length and width plus twice the depth plus overlap at each edge. You also get the pond's volume, the water weight and a pump size based on fish load and waterfall width.
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2 ft for goldfish, 3-4 ft for koi.
For volume. Blank = max depth. With plant shelves, about 2/3 of the max depth.
Liner tucked under edging stones. 1 ft is typical (0.5 ft minimum).
0 if no waterfall. About 150 GPH per inch of width gives a solid sheet of water.
Vertical distance from the pond surface to the top of the waterfall or filter.
How to use the Pond Liner Calculator
- Measure the pond at its longest and widest points and its deepest point, in feet.
- Enter an average depth if the pond has plant shelves or sloped sides, and pick the shape for the volume.
- Set the overlap, the liner that tucks under the edging (1 ft per side is typical).
- Choose the pond use and add a waterfall width, lift and tubing length to size the pump.
- Read the liner size and buy the stock size shown, plus underlayment of the same size.
Pond liner and volume formulas
- Liner length = length + (2 × max depth) + (2 × overlap); liner width = width + (2 × max depth) + (2 × overlap).
- Volume (US gallons) = length × width × average depth (ft) × 7.48. Multiply by 0.785 for oval and round ponds, about 0.8 for freeform shapes.
- Liters = gallons × 3.785; water weighs about 8.34 lb per gallon (1 kg per liter).
- Pump GPH = gallons × turnovers per hour, or 150 × waterfall width in inches, whichever is larger.
Example: a 16 × 10 ft koi pond, 4 ft deep, 3 ft average depth, freeform: liner = (16 + 8 + 2) × (10 + 8 + 2) = 26 × 20 ft; volume = 16 × 10 × 3 × 0.8 × 7.48 ≈ 2,872 gallons; pump at 1.5× = about 4,300 GPH.
Liner sizes for common ponds (1 ft overlap)
| Pond (L × W × max depth) | Liner needed | Stock liner | Volume (rectangle) |
|---|---|---|---|
| 6 × 4 × 1.5 ft | 11 × 9 ft | 15 × 10 ft | 269 gal |
| 8 × 6 × 2 ft | 14 × 12 ft | 15 × 15 ft | 718 gal |
| 10 × 7 × 2 ft | 16 × 13 ft | 20 × 15 ft | 1,047 gal |
| 12 × 8 × 2.5 ft | 19 × 15 ft | 20 × 15 ft | 1,795 gal |
| 15 × 10 × 3 ft | 23 × 18 ft | 25 × 20 ft | 3,366 gal |
| 20 × 12 × 4 ft | 30 × 22 ft | 30 × 25 ft | 7,181 gal |
EPDM rubber (45 mil) is the most common flexible liner and lasts decades; it is fish-safe when labeled as such. Lay the liner on a calm, warm day so it is pliable, fill slowly while smoothing folds, and trim the overlap only after the pond is full.
Frequently asked questions
How do I calculate pond liner size?
Liner length = pond length + 2 × max depth + 2 × overlap, and liner width = pond width + 2 × max depth + 2 × overlap. A 10 × 7 ft pond, 2 ft deep with 1 ft overlap, needs a 16 × 13 ft liner, so buy a 20 × 15 ft stock liner and trim the extra.
How much overlap should a pond liner have?
Leave about 1 ft (30 cm) on every side to tuck under edging stones or bury in a trench. 6 in is the bare minimum; more is safer because soil settles and you can always trim the excess after the pond is filled.
How do I calculate how many gallons are in my pond?
Multiply length × width × average depth in feet to get cubic feet, then multiply by 7.48. For oval or round ponds multiply by 0.785 as well. A 10 × 7 ft pond with a 1.5 ft average depth holds about 10 × 7 × 1.5 × 7.48 ≈ 785 gallons as a rectangle.
What size pump do I need for my pond?
Circulate the whole volume about once an hour for a goldfish pond, every two hours for a plant-only pond and 1.5-2 times an hour for koi. If you have a waterfall, also allow about 150 GPH per inch of spillway width and choose the larger number at your head height.
What is head height for a pond pump?
Head is the height the pump must lift water, plus friction in the tubing. A common rule is to add 1 ft of head for every 10 ft of tubing. Pump flow drops as head rises, so check the pump's flow chart at your head height, not its maximum flow.
Does depth matter for the liner if the pond has shelves?
Use the maximum depth for the liner. The liner has to reach the deepest point and follow every shelf, so planting shelves don't reduce the liner size; they only reduce the water volume.
Do I need an underlayment under a pond liner?
Yes, a geotextile underlayment protects EPDM or PVC liners from roots and stones. It should be the same size as the liner. Old carpet or sand is sometimes used but rots or washes away.
Are all the tools on FreeToolCabin tested for quality and accuracy?
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