How it works
Enter the pond's longest length, widest width and maximum depth. The liner must run down one side, across the bottom and up the other, so the calculator adds twice the maximum depth to each dimension, plus an overlap on each edge to anchor under stones or soil.
This rule works for any shape, including kidney and free-form ponds, because it measures the rectangle that encloses the pond. Shelves and slopes are covered because the maximum depth is used everywhere.
Lay a geotextile underlayment of the same size beneath the liner to protect it from rocks and roots. Fish-safe 45 mil EPDM rubber is the most common choice for garden and koi ponds.
Formula
Liner length = pond length + 2 × max depth + 2 × overlap. Liner width = pond width + 2 × max depth + 2 × overlap.
Questions people ask
How much overlap should a pond liner have?
About 1 foot on every side for a typical pond, which leaves room to bury or stone the edge. Use 1.5 to 2 feet where a stream or waterfall enters.
What liner size do I need for a 10 × 8 ft pond 2 ft deep?
With 1 ft overlap: 10 + 4 + 2 = 16 ft long and 8 + 4 + 2 = 14 ft wide, so a 16 × 14 ft liner.
EPDM or PVC pond liner?
EPDM rubber is more flexible in cold weather, more UV resistant and lasts 20+ years. PVC is cheaper and lighter but stiffens in cold and typically lasts 5 to 10 years.