Pond Liner Calculator
Built by Johnny Alto · free, no sign-up · updated July 26, 2026
Enter your pond's length, width, and maximum depth to find the liner size to buy. The calculator adds twice the depth to each dimension so the liner reaches the bottom and back up, plus an overlap allowance so you have enough to anchor the edges.
Liner size0feet
Total0square feet
The formula adds twice the maximum depth to length and width so the liner drops in and climbs back out, plus your overlap on every side for anchoring under rocks or edging. Add underlayment at the same size to protect the liner.
How to size a pond liner
A flat sheet of liner has to line the bottom, climb both sides, and still have enough left over to anchor at the top. The standard formula takes your pond's length and adds twice the maximum depth, because the liner goes down one side and up the other, then adds an overlap of one to two feet on each side for securing the edge. The width is figured the same way.
So a 10 by 6 foot pond that is 2 feet deep, with a one foot overlap per side, needs a liner about 16 by 12 feet. It is always better to round up, since trimming off excess is easy and coming up short is not.
Do not forget underlayment
Buy underlayment in the same size as the liner. It cushions the liner against roots and sharp stones and dramatically extends its life, especially with cheaper liners. Old carpet or thick landscape fabric works in a pinch, but purpose-made underlayment is inexpensive insurance for a liner you do not want to puncture.
Recommended gear
Build and seal the pond
Frequently asked questions
What size pond liner do I need?
Take the pond's length, add twice the maximum depth, then add your overlap on both sides. Do the same for the width. A 10 by 6 foot pond that is 2 feet deep needs roughly a 16 by 12 foot liner.
How much overlap should a pond liner have?
One to two feet on each side is standard, giving you enough to anchor the edge under rocks, soil, or edging so it does not slip into the pond.
Why add twice the depth?
The liner has to drop down one side, cover the bottom, and rise up the other side, so both the down and up runs add the depth once each, for twice the depth per dimension.
Do I need underlayment too?
Yes, buy it in the same size as the liner. It protects against roots and stones and greatly extends the liner's life.
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This calculator gives estimates for planning only; always confirm against your own measurements and species research. Some links are to our buying guides, which contain affiliate links. As an Amazon Associate I earn from qualifying purchases.
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