Pond Liner Size Calculations

Tips on measuring up your pond

Once you have dug out the hole for your garden pond and are completely satisfied with the shape and size, the next step is to measure the exact dimensions of the hole before ordering your pond liners. The accuracy will help reduce wastage or finding that you haven’t bought enough liner and protective underlay to line your pond, including enough for the overlay.

The overlay dimension added to your calculation depends on how you plan to finish your pond edging. If you are going to use earth to hold the liner in place, add a 30cm overlap to the pond liner size calculations. If you are going to use paving slabs or bricks to hold the liner in place then a 15cm overlap needs to be added to your calculations.

Measuring the Dimensions of a Pond

This is a straightforward process irrespective of whether the pond is kidney, square, rectangular or circular in shape. The following steps should be followed:

  • Measure the longest length of the pond
  • Measure the widest width
  • Take measurement for the deepest depth
  • Now, add one side (Length or Width) to two times the depth plus amount needed for the overlap. It is two times the depth of the pond because the pond liner and protective pond underlay need to go down one side of the pond and back up the other side.
  • Once you have one side (Length or Width), you then need to do the other.

The calculation will look like this:

Length + (2 x Depth) +2” = Total Length of Liner
Width + (2 x Depth) + 2” = Total Width of Liner

Occasionally you may need to round the dimensions up or down because the pond liner you want to order is cut in ‘off a role’ of fixed increments. The dimensions required can be calculated as:

maximum length + (2 x maximum depth of pond) x maximum width + (2 x maximum depth)

To make it easier, in put your dimensions into our Pond Liner Size Calculator in either imperial or metric dimensions to get the exact liner measurements for your pond:

A second suggestion for calculating the correct pond liner size is to use string (and tent pegs to secure the string in place plus a couple of able bodies). The hole for the pond must be dug to completion for this method to work accurately. Take one side of the string and place it six inches to a foot away from the start of the pond hole (at its longest or widest side). Uncoil the string over the pond ledge, down the side, over the bottom, back up the other side and out another six inches to a foot. Cut the string and follow the same procedure for the widest width or longest length, dependent on which was done first. Measure each string using a tape measure. The lengths of each piece of string will be the length and width multiplied together for the pond liner size required.

Measuring L and U-Shaped Ponds

The third method is for unique shaped ponds, such as those in an L or U shape or similar where pond liner dimensions would need careful measurement to reduce wastage. In these circumstances, divide the pond into two or more sections and follow the same process as before. For instance an L shaped pond would be divided into two rectangular parts. The only one difference would be that the depth for the side (length or width) of the pond where the two liners meet only needs to be measured once. This is because the liners will be joined together on the ground. I suggest adding an extra foot or two when doing this type of calculation for the overhang and in case of small errors. Liner seam tape should then be used to seam the liners together.

There are many different pond liners available on the market today. Flexible rubber pond liners are the most commonly used in the industry. They have been trusted for many, many years and come with a life-time year guarantee.


Pond construction and pond liner installation > https://www.pondlinersonline.co.uk/pond-liner-installation