20x20 will do for a 8x10x3 ...you'll have a bit left over that you will trim off...aspear;2330756; said:what size do i need. 15x20? 20x20? 20x25?
If you built a 7 x 12 x 3 pond, you could get a 15x20. That would cover the inside of the pond with 1 foot to overlap the top for anchoring it in place...