How do I calculate the size of my pond liner?

If you are building a new pond or expanding your existing pond, a liner is essential to make your pond watertight and stop water seeping into the ground below. 
Selecting a high quality, durable pond liner is vital. However in order to provide an impermeable seal, it needs to be protected from tears or punctures from sharp objects in the ground beneath the liner, such as stones.

You can achieve this by adding a small layer of sand, concrete or other material on top of the soil where your liner is going to go. Next, we would suggest that you add some underlay to cushion the liner against the ground below and any sharp rocks.
Measuring Your Pond
The shape of your pond is completely down to personal choice and should not be an issue when buying a pond liner. Make sure that when measuring a more unusually shaped pond that you take into account the maximum length, width and depth. Any excess pond liner can easily be trimmed away. 
If your pond depth is sloped, average together the minimum and maximum depth measurements.
To help with calculating your pond liner, we have provided you with a formula that you can easily enter your pond dimensions into. The formula for determining pond liner size is simple:
Overlap + Depth + Width + Depth + Overlap = TOTAL
Overlap + Depth + Length + Depth + Overlap = TOTAL
The two totals will make up the liner size that you need.
  • You will need to round -up if your totals include a decimal (a 3.3 total should be rounded to the closest half meter e.g 3.5 or 4). 
  • Overlap should always be 0.6m (2 feet). This in turn makes the formula:
Metric - 0.6 + Depth +Width + Depth + 0.6 = TOTAL
Metric - 0.6 + Depth + Length + Depth + 0.6 = TOTAL
Imperial - 2 + Depth + Width + Depth + 2 = TOTAL
Imperial - 2 + Depth + Length + Depth + 2 = TOTAL

The Importance of Overlap
Overlap is something that always needs to be taken into account for any pond feature. You will need the extra 0.6m (2ft.) so that the liner to secure to the ground. If not secured properly, the liner will sink into the pond and expose the sides when you start to fill the pond. We advise you to gently adjust the pond liner as it is being filled in order to smooth out any creases that can form in the process. 
Adding water adds considerable weight to the pond liner. This is why edging the pond correctly with something heavy, like pavement or rock, is so important in order to keep your pond liner in place.
Pond Liner Calculation: An Example
To help demonstrate this, here is an example. Let’s say you have a koi pond that is 1.2m long, 1.5m wide and 0.7m deep. Here is what your formula will look like:
0.6 + 0.75 + 1.5 + 0.75 + 0.6 = 4.2m
0.6 + 0.75 + 1.2 + 0.75 + 0.6 = 3.9m
Given the totals above, you will need a 4.5 x 4 or 5 x 4 pond liner and underlay.

If you would like any further advice, or recommendations on the most suitable liner for your pond, please contact our customer services team who will be happy to advise further.