Pond Liner:
Materials, Sizes
& Calculator

For most garden and koi ponds, 45 mil EPDM rubber: flexible, fish-safe and typically warrantied for 20 years. RPE is better for large farm ponds where weight and cost matter and the liner can be covered. Spray-on polyurea is best for irregular shapes, concrete ponds and potable water.

Liner length = pond length + (2 × maximum depth) + 2 ft, and liner width = pond width + (2 × maximum depth) + 2 ft. For a 10 × 8 ft pond that's 3 ft deep: (10 + 6 + 2) × (8 + 6 + 2) = 18 × 16 ft. Round up to the next stock size.

EPDM typically lasts 20–30+ years, butyl 20+ years, HDPE 36–50 years when covered, RPE 10–20 years buried but only a few years exposed, and PVC up to 20 years buried but about 2 years in direct sun. Concrete can last 50+ years if it doesn't crack.

45 mil EPDM is the standard for residential ponds and is enough for most installations with a proper underlayment. Use 60 mil where rocks, roots or heavy foot traffic are a concern. RPE is commonly used at 20–40 mil.

Yes. A non-woven geotextile of about 8–16 oz per sq yd protects the liner from rocks and roots. Overlap underlayment seams 6–12 inches. It typically costs $0.25–$0.40 per sq ft.

Liner material runs roughly $0.30–$0.90 per sq ft for PVC, RPE and HDPE and $0.75–$2.50 for EPDM. HomeGuide puts typical installed pond liner projects at $300–$7,400, or about $0.50–$3.50 per sq ft installed, and $10,000–$22,500 to line a one-acre pond.

EPDM is more flexible, easier to fold into small shaped ponds and tolerates sun better. RPE is much lighter (a 20 × 16 ft sheet weighs roughly 60–80 lb vs about 200 lb in EPDM), cheaper per square foot and available in huge panels, but should be covered.

For EPDM, overlap at least 3 inches, clean and prime both surfaces, apply 3-inch double-sided seam tape, roll it down and cover the seam with a 6-inch cover strip. Seams are the most common sheet-liner leak point, so avoid them where possible.

Multiply length × width × average depth in feet, then × 7.48. For a circle, use 3.14 × radius² × average depth × 7.48. For irregular ponds, average several measurements and use about 7 gallons per cubic foot.

Often, yes. Spray polyurea can be applied over cleaned concrete or block, or over geotextile in an earthen pond. Leaking concrete ponds and fountains are a common job. An applicator will check the substrate and prep before quoting.