How this calculator works
Multiply the chosen plan area by measured average water depth. Sample depth across the pond rather than treating the deepest point as the average. For a liner estimate, add twice maximum depth and twice the edge allowance to each maximum plan dimension. This estimates a rectangular sheet, including offcuts around curved ponds. Shelves, irregular contours, anchoring trenches and waterfalls can require extra material, so measure the excavated surface before purchasing.
Formula
V = plan area x average depth; rectangle area = LW; ellipse area = pi LW/4; circle area = pi D^2/4; right triangle area = LW/2; liner length = maximum length + 2 x maximum depth + 2 x edge allowance, similarly for width.
Worked example
A 4 x 3 m rectangular pond averaging 1 m deep holds 12 m3. At 1 m maximum depth and 0.5 m edge allowance, estimate a 7 x 6 m liner sheet: 42 m2. At $10/m2, liner cost is $420; water at $2/m3 costs $24.
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Frequently asked questions
Why are average and maximum depth separate?
Average depth estimates water volume. Maximum depth helps allow enough sheet to reach the deepest portion of the pond.
Does triangle mode support every triangle?
It uses a right triangular plan whose perpendicular legs are the length and width. For other outlines, divide the pond into measured areas.
Is the liner sheet size exact?
No. It is a planning allowance based on maximum dimensions. Confirm contours, shelves, seam positions and anchoring requirements on site.