Pond liner calculator
The liner must drape the hole and still reach over the rim. Enter your pond's size and depth — get the sheet size to order, the water gallons for pump sizing, and what it costs.
Liner size
What size pond liner do I need?
The liner has to run down one wall, across the bottom, up the other wall, and still overhang the rim by a foot on every side to be anchored. The universal formula:
Worked example: a 10 × 6 ft pond, 2 ft deep: liner = (10 + 4 + 2) × (6 + 4 + 2) = 16 × 12 ft — 192 ft² of liner. A 10 ft circle, 2 ft deep: (10 + 4 + 2) = 16 × 16 ft, 256 ft².
Liner materials
| Material | Lifespan | Price / ft² | Note |
|---|---|---|---|
| 45 mil EPDM rubber | 20–40 yrs | $0.70–$1.20 | The standard — flexible, fish-safe, patches easily |
| RPE (reinforced polyethylene) | 20+ yrs | $0.50–$0.90 | Stronger per mil, stiffer, harder to fit corners |
| PVC | 5–10 yrs | $0.40–$0.70 | Cheap, becomes brittle; OK for temp ponds |
Water volume for pump sizing
Gallons = length × width × depth × 7.48 (the calculator shows it automatically). Pumps should circulate the full volume about once per hour — a 900 gal pond wants an 800–1,200 GPH pump, and koi ponds double it. Water weighs 8.34 lb/gal, so a 900 gal pond holds over 3.5 tons — the shelf it sits on needs compacted, undisturbed soil.
Digging tips that save liner
Cut shelves 8–10 in deep around the rim for marginal plants, slope sides at ~20° (1:3) so stone doesn't slide, and dig the hole 2 in deeper than planned to bed a sand cushion. Check the level with a string line across the hole before the liner drops — a ½-inch lip shows as a permanent waterfall.