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How to Size a Pond Liner

working with rock and pond liner in partially filled pond

You've been dreaming of the perfect koi pond for quite some time, and now you're ready to make the plunge. Congrats, and may we say, "Welcome to the world of backyard water gardens!"

One of the first questions you will have when building a pond is, "How much pond liner do I need?" Keep reading to learn how to measure for a pond liner.

How much pond liner do I need?

While you may find a pond liner calculator somewhere on the web, you don't need one. The pond liner calculation formula is easy. Let's walk through it, and get the pond liner size you need.

To get your pond liner measurements you will first need three of your pond dimensions: your pond's maximum length, maximum width and maximum depth. Take these measurements in feet.

Calculating the length you need

You’ll add the length to two times the depth plus 2. You use two times the depth because the liner needs to go down on both sides. The extra two feet is for overhang. This gives you one extra foot on each side.

The length calculation looks like this: Pond Length + (2 x Max Depth) + 2 = Length of Liner

Calculating the width you need

Calculating your pond liner width works the same way. You’ll add the width to two times the depth plus 2. You use two times the depth because the liner needs to go down on both sides. The extra two feet is for overhang. This gives you one extra foot on each side.

The width calculation looks like this: Pond Width + (2 x Max Depth) + 2 = Width of Liner

Additional Considerations & Tips

The calculations above will work great for circle, kidney bean and natural organic shaped ponds. However, if you have an L shaped pond you may want to take an alternate approach to calculating the size, so you don't waste any liner.

L Shaped Ponds

With an L-Shaped pond, we recommend segmenting your pond measurements into two rectangles before running calculations. Take these two sets of measurements and use the calculations above to determine the two pond liner sizes you need. Keep in mind you will be purchasing two liners with this approach, and will need to make a seam. We offer complete seaming kits that include everything you need.

When done properly, a chemical bond occurs during the process that makes the seam stronger than the liner itself!

EPDM Rubber Liner

Material matters when it comes to pond liner. Remember, your pond liner will serve as the permanent foundation for your garden pond.

EPDM rubber is the choice material of industry professionals, and the material that we most highly recommend. EPDM is the most resilient and will last the longest. 45 Mil is the thickness that most people use. You can shop a wide range of 45 mil EPDM liners on our website.


Don't skip pond underlayment. Adding a protective barrier between the earth and your pond liner can help prevent holes and leaks, and will give you peace of mind. You can purchase the same square footage of underlay that you purchase for your pond liner. You can even use it inside the pond for protection under heavy stones.

We recommend lining the entire pond bottom with underlay, but especially don't skip the sides. You can cut the material into strips and overlap it slightly. Some customers use duct tape to join them, but there is no need to seam underlay together.

Before you position your underlay, add a few inches of raked all-purpose sand on the bottom of the pond. This will add an extra layer of cushion.

Pond Liner Application Tips

When laying out your pond liner there are a few quick tips to help. In corners you can make folds like wrapping paper but in reverse. This is helpful for formal ponds with hard edges, but you can use this to some degree in natural shaped ponds, too. With any extra material just pull it up at the top, fold it back and tuck it underneath itself.

Before you do any rocking, work the liner until all creases and wrinkles are out. Get in the pond and walk over the liner making sure it's all pulled and pushed down well. Do this before you add rocks or water, or they will pull the liner down during design and fill-up.

Fill up the pond half-way before you start rocking. Otherwise, rocks at the top may be pulled into the pond as the liner expands with the weight of the water.

Pro-tip: If your pond liner has been folded or rolled up, lay it out and the heat will make the material more pliable to work with, but be aware it does get hot! Wear gloves and keep your shoes on when handling or walking on liner to protect your hands and feet.

In Summary

We hope this post has helped you learn how to calculate pond liner size. And hopefully you've gathered a few extra tips along the way.

We love helping customers on their pond journeys. Please reach out to our team if you have any questions. We have highly trained pond techs that will be happy to assist!

Article Posted: 02/20/2024 11:49:46 AM

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