Pond Liner Calculator

Measure the longest length, the widest width and the maximum depth. Then liner length is length + 2 x depth + 2 ft, and liner width is width + 2 x depth + 2 ft, the Kansas State University formula. A 10 × 8 ft pond that is 2 ft deep needs a 16 × 14 ft liner, which is 224 sq ft.

Liner length equals pond length plus twice the depth plus the overlap. Liner width equals pond width plus twice the depth plus the overlap. The depth is doubled because the liner runs down one side and up the other. With the 2 ft overlap in total from Kansas State, a 15 × 10 × 3 ft pond needs 15 + 6 + 2 = 23 ft by 10 + 6 + 2 = 18 ft.

Kansas State University advises laying the stone border so the liner sits slightly higher than the surrounding ground. Put a layer of stone down first, then the liner, then another layer of stone. Make sure the liner is in place and secure before trimming the edges, and leave the trimmed edge tucked under the stone so it cannot be seen or catch the sun.

A tarp is made as a temporary cover, not as a permanent water barrier. Kansas State University describes water garden liners as flexible, UV-treated rubber of 40 to 45 mil. A tarp may leak, split in the sun or be unsuitable for fish and plants, so read its label. For a permanent pond, use a liner sold for ponds and ask the maker if it is safe for fish.

No honest single figure exists, because life depends on the material, the sun, how well the liner is protected and how it is installed. Wikipedia notes that properly formulated EPDM can be used outdoors for many years or decades. Check the warranty term of the product you buy. Underlayment, no sharp stones and a buried or covered edge all help the liner last.

Kansas State University adds 2 ft in total, which is 1 ft on each side, and also suggests an 18 to 24 inch margin around the edge of the pond for stone. More overlap costs more but gives room to anchor and trim. For a 10 × 8 × 2 ft pond each extra foot of overlap adds about 31 sq ft of liner.

Use the longest length and the widest width of the shape, as if it sat in a rectangle, plus twice the maximum depth plus the overlap. Kansas State University says to use the widest spot for each. The liner then fits any outline inside that box, with extra folded away in the corners. A 12 × 9 ft kidney that is 2.5 ft deep needs 19 × 16 ft.

Use the maximum depth. The liner has to reach the deepest point and come back up, and a liner sized on the average depth will pull tight over the deep end. For a 10 × 8 ft pond with a 3 ft deep end and a 1.5 ft average, the correct liner is 18 × 16 ft, while the average would give 15 × 13 ft.

Kansas State University says to adjust the formula for hills and waterfalls without giving a number. The calculator adds a separate piece for the run: length plus overlap by width plus twice the channel depth plus overlap. A 10 ft run that is 1.5 ft wide and 0.5 ft deep needs 12 × 4.5 ft, or 54 sq ft. Treat it as an allowance.

Underlayment is a fabric laid under the liner to protect it from stones and roots. Wikipedia describes geotextiles as permeable fabrics that give protection among other functions, and Kansas State University covers the bottom and walls with a sheet of it. The calculator sizes it as (length + 2 x depth) × (width + 2 x depth), which is 168 sq ft for a 10 × 8 × 2 ft pond.

After. Kansas State University says to always dig the hole before buying the pond liner, because a pond rarely ends up exactly as drawn. Dig, shape the shelves, remove stones and roots, then measure the longest length, widest width and deepest point of the real hole. Use those numbers in the calculator, and add a little for settling and trimming.

For a depth of 2 ft the liner is 16 × 14 ft with the standard 2 ft overlap in total. At 3 ft deep it is 18 × 16 ft, and at 1.5 ft deep it is 15 × 13 ft. Depth changes the answer more than most people expect.

Use the same formula in metres. Choose the metric option, enter the length, width and depth in metres and a 0.6 m overlap in total. A 4 × 3 m pond that is 0.7 m deep needs 6.0 × 5.0 m, or 30.0 sq m. The calculator rounds each side up to the next half metre for ordering, a common way pond liners are sold in the UK and elsewhere.

Kansas State University says water garden liners are 40 to 45 mil, flexible and UV-treated. A mil is a thousandth of an inch, so 45 mil is about 1.1 mm. Thicker liners resist punctures better and cost more, and larger or deeper ponds, or sharper ground, may justify a heavier grade. Use the maker's advice for your ground and your fish.

Lay the liner with plenty of slack and let it settle into the hole. Kansas State University says folds are normal, and that a few large folds placed out of view look better than many small ones. Fill the pond slowly and smooth and fold the liner as the water rises. Do not stretch it tight, because water weight will pull it into the corners and pull it off the edge.

Yes. Kansas State University notes that ponds can also be made from plastic or fiberglass preformed liners or from concrete. A preformed shell has a fixed size and depth, so you choose the shell and dig to fit it, and there is no liner to size. Use this calculator when you want a flexible liner and a free shape.

Prices vary by material, thickness and maker, so the calculator uses your own price per square foot or per square metre. With a placeholder of $1.25 per sq ft, a 16 × 14 ft liner (224 sq ft) costs $280, and underlayment at $0.35 adds $59. Get a quote for the exact size.

Some makers sell seaming tape or splice kits for joining sections, and some say a single piece is best. This depends on the material, so follow the maker's own instructions and do not improvise a join under water. If a single piece is much too large to handle, ask the supplier whether they can weld or supply a made-up size.

Not by much. A shelf is part of the shape, so the liner still follows the bottom and walls. Use the maximum depth of the deepest zone and the longest and widest points, as Kansas State does, and allow for the extra material that steps take up. If your pond has many deep steps, add a small extra percentage in the calculator.

It makes the liner longer and wider by that percentage, as a margin for steps, folds or a hole that comes out larger than planned. With 10 percent, a 20 × 14 × 3.5 ft pond goes from 29 × 23 ft to 31.9 × 25.3 ft before rounding. It is zero by default, because the formula already has an overlap.