A 10 × 8 ft pond, 2 ft deep with a 1 ft overlap, needs a 16 × 14 ft liner (224 sq ft), so you would buy a 20 × 15 ft liner and the same size underlayment. It holds about 1,197 gallons and needs a pump of at least 1,200 gph.
How the pond liner calculator works
PondLinerCalc sizes the liner so it reaches the bottom of the deepest point on both sides and still overlaps the edge: liner length = pond length + 2 × maximum depth + 2 × overlap, and the same for the width. It then rounds each side up to the next 5 ft (or 1.5 m), the steps most EPDM and PVC liners are sold in, and suggests underlayment of the same size. Volume is length × width × average depth, multiplied by π/4 for round or oval ponds, at 7.48 US gallons per cubic foot or 1,000 litres per cubic metre. The pump should turn that volume over once an hour, or twice for koi.
Pond liner sizes for common ponds
Rectangular ponds with a 1 ft overlap each side.
| Pond | Depth | Liner needed | Gallons |
|---|---|---|---|
| 6 × 4 ft | 1.5 ft | 11 × 9 ft | 269 |
| 8 × 6 ft | 2 ft | 14 × 12 ft | 718 |
| 10 × 8 ft | 2 ft | 16 × 14 ft | 1,197 |
| 12 × 10 ft | 3 ft | 20 × 18 ft | 2,693 |
| 15 × 10 ft | 3 ft | 23 × 18 ft | 3,366 |
| 20 × 15 ft | 4 ft | 30 × 25 ft | 8,977 |
Frequently asked questions
How do I calculate pond liner size?
Liner length = pond length + 2 × maximum depth + 2 × overlap; liner width = pond width + 2 × maximum depth + 2 × overlap.
How much overlap should a pond liner have?
About 1 ft (30 cm) on each side to tuck under edging stones and allow for settling.
Do shelves change the liner size?
No. The liner still has to reach the deepest point, so use the maximum depth; shelves only reduce the volume.
Is PondLinerCalc free?
Yes, with no sign-up or ads, and your pond details stay in your browser.
Should I buy a bit bigger than calculated?
Yes. Measure the dug hole, not the plan, and round up: a liner that is too small cannot be fixed, while extra can be trimmed.