Pond and reservoir liner calculator
Enter the top dimensions, the depth and the batter slope. It returns the sheet size required, the area including waste, the roll count at your chosen thickness and an approximate seam length.
Estimate
How the figure is worked out
A lined basin is not a flat rectangle. The liner covers the floor, climbs both batters in each direction, and carries on past the crest into the anchor trench. Every one of those adds sheet.
The floor is smaller than the top opening, because the batters slope inward. On a 1:2 slope at 3 m deep, each batter eats 6 m horizontally, so a 50 m top length gives a 38 m floor.
The sloped face itself is longer than the depth. At 3 m deep on a 1:2 slope the batter face measures about 6.7 m, not 3 m, because it is the hypotenuse. Missing this is the commonest reason a liner order comes up short.
So the sheet required in each direction is the floor dimension, plus two batter faces, plus two anchor allowances. Multiply the two directions for area, add waste, and divide by roll area for the roll count.
The seam figure is the interesting one
Seam length tells you how much welding the job actually contains, which drives crew size, machine hours and programme far more directly than area does. Feed it into the seam and welding time calculator to convert it into days.
Frequently asked questions
How much liner do I need for a pond?
More than the surface area of the water, which is the mistake most people make. Liner has to cover the floor, run up every batter slope, and continue into an anchor trench at the top. For a basin with sloped sides, the sheet needed in each direction is the floor dimension plus twice the sloped face length plus twice the anchor allowance. The calculator above does that arithmetic, including a waste allowance for cutting.
What waste allowance should I use?
Five percent is a reasonable default for a simple rectangular basin with clean geometry. Raise it to eight or ten percent where the shape is irregular, where there are many penetrations, or where the batters change slope, because every cut produces an offcut that cannot be used elsewhere. Below five percent you are assuming a perfect panel layout with no errors, which rarely survives contact with a site.
How deep should the anchor trench be?
Design decides it, and it varies with wind exposure, liner thickness and whether the liner is covered. A common arrangement is a trench roughly 500 mm deep and 500 mm wide, set back from the crest, with the liner running down into it and backfilled. The calculator's anchor allowance is the extra sheet length beyond the crest, so around 1.0 to 1.5 m per side covers a typical trench plus the run-out to it. Use the figure from your drawings where you have one.
Does the calculator account for the anchor trench and overlaps?
The anchor allowance is a field you set, applied to both sides in both directions. Panel overlaps are accounted for in the seam and panel figures, which assume a 100 mm overlap on a 7 m roll, giving an effective panel width of 6.9 m. What it does not do is optimise the panel layout, so treat the roll count as a budget figure rather than a purchase order.
Which thickness should I select?
The design engineer sets it. As orientation, farm ponds and water pans are usually 0.75 mm or 1.00 mm, irrigation reservoirs and effluent lagoons 1.00 mm to 1.50 mm, and mining or landfill work 1.50 mm and above. Changing the selection here only changes the roll count, because roll length falls as thickness rises. Full properties per grade are in the specification table.
If you are still working out what the project needs, start from our overview of the machine range.
Turn the estimate into a quotation
Send the dimensions or a drawing and we will do a proper take-off, then quote liner, welding machines and consumables against it.