PONDPOISE

Pond Liner Size Calculator

Enter your planned pond's length, width, and depth to get the liner sheet size you need to order, in feet and square metres, before you break ground.

For a round pond, use the diameter for both length and width.
Extra material left over for anchoring the edges. 2 ft is a common default.

Liner size needed

Liner length (ft)
16
Liner width (ft)
12
Area (sq ft)
192
Area (sq m)
17.84

How the sizing formula works

The standard formula is: liner length = pond length + (2 × depth) + overlap allowance, and liner width = pond width + (2 × depth) + overlap allowance. Multiply the two together for the total area to order.

This is a planning estimate for buying material, not a substitute for measuring the actual excavation once it's dug — real holes rarely come out exactly to plan, so it's common to round up to the nearest standard liner size a supplier offers.

Frequently Asked Questions

Why do I add depth twice, not once?

The liner has to travel down one side wall, across the bottom, and back up the opposite side wall. That means each dimension (length and width) picks up two depth's-worth of extra material, not just one.

What is the overlap allowance for?

Once the liner lines the hole, you still need extra material at the top edge to anchor it — tucked under coping stones, buried in a trench, or folded back and pinned down. The overlap allowance (commonly around 2 feet) covers that edge margin so you're not short by the time you reach the rim.

Does this work for an irregular-shaped pond?

It works best as a starting estimate for the bounding rectangle of any pond shape, including round or irregular ones — measure the longest length and widest width the pond will reach, and use those. For a very irregular shape, add a little extra margin beyond the calculated figure, since offcuts from corners and curves aren't reusable elsewhere.

What liner material should I buy?

This calculator only sizes the sheet — it doesn't recommend a specific material. EPDM rubber is a common, durable, fish-safe choice for garden ponds; whatever you choose, confirm it's rated fish-safe before it goes in the water.

Planning estimate only. Re-measure the finished excavation before ordering, and round up to your supplier's next standard liner size to leave margin for error.