We have a fish pond and we need a new liner But we don’t know how big is the pond. How can we measure it?

Easy to measure. Take the depth of the pond in the deepest part and multiply by 2 + 1 foot. Then add this measurement to each side measurement. Liners start at 10′ and go up by 5 feet. So if you need a 12 x 16 you would have to order a 15 x 20.