How to use this calculator
Start by selecting your pond shape: rectangle, circle, or kidney/freeform. Enter the maximum length and width (or diameter for circular ponds), along with the maximum depth. The calculator adds the depth and overlap to each dimension automatically to determine the total liner size.
You can optionally add a shelf or ledge, which is a shallow step around the inside edge of the pond for planting. Adjust the overlap amount if you want more or less material around the edges. Finally, choose your liner material to see cost estimates based on typical pricing per square foot.
Pond liner sizing formula
Liner length = pond length + (2 x maximum depth) + (2 x edge overlap). This accounts for the liner going down one side, across the bottom, and up the other side, with extra material on both ends for securing under rocks or edging.
Liner width = pond width + (2 x maximum depth) + (2 x edge overlap). The same principle applies in the width direction.
For circular ponds, use the diameter in place of both length and width. For kidney or freeform shapes, measure the longest and widest points of the overall shape and use those as your length and width values.
Frequently asked questions
How do I calculate what size pond liner I need?
Measure the maximum length, width, and depth of your pond. Add twice the depth and twice the overlap to both the length and width. For a pond that is 10 ft long, 8 ft wide, and 3 ft deep with 1.5 ft overlap, you would need a liner 19 ft long and 17 ft wide.
What is the best pond liner material?
EPDM rubber (45 mil) is the most widely recommended material for garden and koi ponds. It is flexible, UV resistant, fish safe, and lasts 20 to 30 years. PVC works well for smaller or temporary ponds. RPE (reinforced polyethylene) is best for very large ponds because it is lightweight and strong.
Do I need underlayment under my pond liner?
Yes. Underlayment (geotextile fabric) goes beneath the liner to protect it from rocks, roots, and debris in the soil. It is inexpensive compared to the liner itself and can prevent costly puncture repairs. Cut it to the same dimensions as your liner for full protection.
How much overlap should I leave around the edges?
Plan for at least 1 foot on each side, though 1.5 to 2 feet is standard. The overlap allows you to secure the liner under rocks, pavers, or edging material. Extra overlap also helps prevent water from seeping behind the liner during heavy rain.