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Pond Liner Calculator

Updated How we build and test

What size pond liner do you need? Enter your pond length, width and deepest point to get the liner size, including overlap for the bank.

Liner that sits on the bank under the edging. 1–2 ft is usual.

$ / ft²

Liner size needed

Enter the pond size and depth to see what size liner to buy.

How to use the pond liner calculator

  1. Measure the pond at its longest and widest points, and the depth at the deepest spot.
  2. Set the overlap — the liner that sits on the bank under your edging stones. 1 to 2 ft each side is usual.
  3. Read the liner size and round up to the next size your supplier stocks.
  4. Enter a price per square foot for a cost estimate.

Formulas

Liner length = pond length + (2 × depth) + (2 × overlap)
Liner width = pond width + (2 × depth) + (2 × overlap)
Liner area (ft²) = liner length × liner width

The depth is doubled because the liner has to drop to the bottom on one side and climb back out on the other. This is the standard formula, and it deliberately ignores shelves and sloped sides — those use a little less liner, so the result errs on the generous side, which is what you want when the alternative is a liner that will not reach.

Worked example: a 10 × 8 ft pond, 3 ft deep

  1. Liner length: 10 + (2 × 3) + (2 × 2) = 20 ft.
  2. Liner width: 8 + (2 × 3) + (2 × 2) = 18 ft.
  3. Liner area: 20 × 18 = 360 ft².
  4. Approximate volume: 10 × 8 × 1.8 ft average depth × 7.48 = about 1,080 gallons.

Why the extra is not waste

It is tempting to trim the overlap down to save money, but the liner edge has to sit above the water line all the way round, held under stone or soil. If it dips anywhere, water wicks out of the pond and the level drops for reasons that are very hard to find later. Buy the size the calculator gives and trim on site once the pond is full.

Quick reference

Pond size 2 ft deep 3 ft deep 4 ft deep
6 × 4 ft 14 × 12 ft 16 × 14 ft 18 × 16 ft
8 × 6 ft 16 × 14 ft 18 × 16 ft 20 × 18 ft
10 × 8 ft 18 × 16 ft 20 × 18 ft 22 × 20 ft
12 × 10 ft 20 × 18 ft 22 × 20 ft 24 × 22 ft
16 × 12 ft 24 × 20 ft 26 × 22 ft 28 × 24 ft

Liner sizes include 2 ft of overlap on each side.

Questions

What size liner do I need for a 10 × 8 ft pond?

At 3 ft deep with 2 ft of overlap each side, you need a 20 × 18 ft liner, which is 360 ft².

How do you calculate pond liner size?

Add twice the depth and twice the overlap to both the length and the width. The depth counts twice because the liner goes down one side and up the other.

How much overlap does a pond liner need?

1 to 2 ft on each side. The edge has to sit above the water line, held down by stone or soil, all the way around.

How many gallons is my pond?

Multiply length × width × average depth in feet, then by 7.48. Average depth on a dug pond with sloped sides is roughly 60% of the deepest point.

What size liner for a 6 × 4 ft pond, 18 in deep?

Add twice the depth plus 1 ft of overlap each side: (6 + 3 + 2) × (4 + 3 + 2) = an 11 × 9 ft liner.

Sources

  1. NIST Guide to the SI, Appendix B.8: Factors for units listed alphabetically, National Institute of Standards and Technology.
    Used for: Exact inch, foot and gallon definitions and the metric conversions.

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