Estimating the size of your pond liner is a very important step. You will want to use one continuous piece if possible. Fitting and taping pieces together may lead to leaking if done incorrectly. You will also want to be sure you have enough overlap all around the perimeter of your pond to go under your edging and again, help ensure that there are no leaks around the edge.
I encourage you to find a reliable, professional pond supplier near you. They can be a great resource for all your pond questions. It can be especially helpful to have such a resource nearby if this is your first backyard pond.
It is important to purchase a heavy duty rubber liner that is fish-safe and UV ray resistant. It is recommended that the thickness be .45 mil. This type of liner typically has a 20 yr. life expectancy. If you are shopping around for a liner, I encourage you to read the fine print. Not all liners are the same and some are made of thinner, less durable materials.
Before we begin, take the longest and widest lengths of your pond layout. Then, draw a square or rectangle that will completely enclose that shape. This will give you the (L)ength and (W)idth of your design. Convert the (D)epth of your pond into feet. Most backyard ponds are 18″ – 24″ or 1.5′ – 2′ D.
The formula for estimating the size of your pond liner is:
Length of the liner = L+2(D)+2
Width of the liner= W+2(D)+2
Note: all units are measured in feet
My pond is 11′ L x 8′ W x 1.5′ D
So my formula looked like this:
11′ +3’+2′ = 16′
8’+3’+2′ = 13′
So, I needed a liner that was 16′ x 13′. The standard size liners came in 15′ x 15′ or 15′ x 20′. Therefore, I purchased a 15′ x 20′ liner to fit the size of my pond.