How Much Pond Liner Do I Need?
One of the most common questions we get from people planning a DIY pond or water feature is how much liner to order. Get it right and you have a clean, professional install with no joins. Get it wrong and you're either buying more liner or - worse - you run short mid-build.
The good news is the calculation is straightforward once you know the formula. Here's how it works.
If you're still deciding between liner types, our EPDM vs PVC guide covers everything you need to know before you buy.
The Basic Formula
Pond liner needs to cover not just the base of your pond, but also the sides and a folded edge at the top for anchoring. The standard formula for calculating liner size is:
Liner Length = Pond Length + (2 x Pond Depth) + (2 x Overlap)
Liner Width = Pond Width + (2 x Pond Depth) + (2 x Overlap)
Where overlap is the amount of liner that folds over the edge of the pond - typically 300mm (0.3m) on each side.
A Worked Example
Let's say you're building a pond that is:
3m long
2m wide
0.6m deep
Using the formula:
Liner Length = 3 + (2 x 0.6) + (2 x 0.3) = 3 + 1.2 + 0.6 = 4.8m
Liner Width = 2 + (2 x 0.6) + (2 x 0.3) = 2 + 1.2 + 0.6 = 3.8m
So for this pond you'd need a piece of liner at least 4.8m long by 3.8m wide. In this case the 6.10m wide roll would cover the width with room to spare, and you'd order 4.8 lineal metres.
What About Irregular Shapes?
If your pond has curves, shelves, or an irregular shape, the formula still works - you just use the maximum length and maximum width of the pond. The liner is flexible enough to fold and tuck around curves without needing to be cut to an exact shape.
For very complex shapes or large features it's worth adding an extra 10-15% to your calculation as a buffer. You can always trim excess - you can't add more once the liner is cut.
Don't Forget the Overlap
The overlap is the bit people most commonly underestimate. 300mm on each side is the minimum - enough to fold over the pond edge and tuck under the coping stones or surround. For larger or deeper ponds, 450mm gives you more flexibility during the build.
If you're installing the liner yourself for the first time, err on the side of a larger overlap. It's much easier to trim back excess than to discover you're short once the pond is built and filled.
Available Widths
Firestone ELEVATE EPDM pond liner from Southern Waterscapes is available in four widths:
3.05m wide - $125.00/lm
6.10m wide - $249.00/lm
9.15m wide - $375.00/lm
12.20m wide - $499.00/lm
For most residential garden ponds, the 3.05m or 6.10m width will cover the pond width in one piece with no joins required. Larger features may need the 9.15m or 12.20m roll - or in some cases, two pieces joined with EPDM tape.
Do You Also Need Geotextile Underlay?
Yes - and this is important. Firestone ELEVATE EPDM liner carries a 20-year manufacturer's warranty, but only when installed correctly with geotextile underlay underneath and over the liner. The underlay protects the liner from punctures caused by stones and soil movement, and is required for the warranty to be valid.
You'll need underlay in the same dimensions as your liner. Our Geotextile Pond Underlay is 3.9m wide and sold per lineal metre - order the same quantity as your liner and cut to suit.
Use Our Free Liner Calculator
Rather than doing the maths by hand, use the free EPDM Liner Calculator on our product page. Enter your pond length, width, depth, and overlap and it will calculate your required liner dimensions, recommend the right roll width, and give you an estimated price including GST.
Calculate your liner size here
Once you know what you need, use the enquiry form on the same page to place your order. We'll confirm freight cost based on your location and cut your liner to size.
A Note on Pondless Waterfalls
The same formula applies to pondless waterfalls, with one difference - you're lining a reservoir basin and a waterfall run rather than a traditional pond shape. The waterfall run is typically measured as a long, narrow strip, and the basin as a separate rectangular shape. If you're not sure how to calculate liner for a pondless waterfall, get in touch and we can help work it out before you order.
Order EPDM Pond Liner NZ-Wide
Firestone ELEVATE EPDM liner is available from the Southern Waterscapes online store, cut to your required size and shipped from our North and South Island warehouses. Freight is calculated per order based on liner size and delivery location.
Southern Waterscapes Ltd - New Zealand's only Certified Aquascape Contractor, based in Rolleston. Aquascape products and Firestone EPDM liner available nationwide from our online store.