It needs a 22 × 20 ft liner, holds about 3,591 gallons and calls for a pump of at least 7,200 gph. A common stocking guide is about 250 gallons per adult koi, so this pond suits around 14 fish.
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 deep should a koi pond be?
At least 3 ft, and 4 ft or more in cold climates or where herons visit.
How many koi per gallon?
A common rule is one adult koi per 250 gallons, with the first fish needing about 1,000 gallons.
What liner is best for koi?
45 mil EPDM rubber is the usual choice; it is fish-safe, flexible and lasts for decades.
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.