Pond Liner Calculator — What Size Pond Liner Do I Need?

The formula for pond liner size is: Liner length = Pond length + (2 x Maximum depth) + 600mm overlap. Apply the same formula to the width. The overlap allows 300mm on each side for securing the liner at the edge. For a pond that is 3m long, 2m wide and 0.6m deep, you need a liner at least 4.8m x 3.8m.

Yes, pond underlay (also called protective fleece) is strongly recommended under every pond liner. It protects the liner from punctures caused by stones, roots, and sharp objects in the soil. Underlay should be the same size as the liner. The cost of underlay is minimal compared to the cost of repairing or replacing a damaged liner.

EPDM rubber — and the closely related but distinct butyl rubber — is the best pond liner material for UK garden ponds. EPDM (ethylene propylene diene monomer) is the more durable and now the more common choice; butyl (isobutylene-isoprene) is similarly flexible but physically weaker and easier to puncture. Both are flexible and UV-resistant and typically last 25-50 years. Standard thickness is 0.75mm for garden ponds, or 1.0mm for large or koi ponds. PVC liners are cheaper but have a shorter lifespan of 10-15 years and become brittle in cold weather.

Allow at least 300mm (12 inches) of overlap on all sides of the pond. This excess liner is used to secure the edge using rocks, paving slabs, or turf. Our calculator adds a total of 600mm (300mm per side) to both the length and width dimensions. For wildlife ponds with gently sloping edges, you may want to add extra. Use our Pond Volume Calculator to work out pump and filter sizes.

For a circular pond, calculate the liner as a square: diameter + (2 x depth) + 600mm overlap. For example, a circular pond 2m in diameter and 0.5m deep needs a liner at least 3.6m x 3.6m. You cannot use a circular liner — you need a square piece that is large enough to cover the entire circle with overlap.