Home Depot is horrible as far as liner is concerned. I believe it is only 25 mil thick, and guaranteed for 10 years. And as far as you are concerned The_Tominater, yes, you want to allow a few extra feet on each side of the pond worth of liner, along with going all the way to the bottom and up the other side, again leaving a few extra feet around the perimeter of the pond. The one way to calculate liner size is:
Maximum Length, Plus 2 X Maximum Depth, Plus 2 Feet
-and then-
Maximum Width, Plus 2 X Maximum Depth, Plus 2 Feet
Or, you can run a tape measure from one end, down along the sides, over the bottom, and back up the other side, doing this for both width and length.
You may want to check the link that PondMom gave, or check
www.eponds.com. They usually will give you free shipping on all orders over $25. Check around, patience is a virtue. Sometimes, I tell my customers that:
The bitterness of poor quality long remains after the sweetness of a low price is forgoten. Check around, and then check back here and let me know how it goes!
Just A Thought...