How to calculate the amount of liner & underlayment needed?

[MJK]

Pond is 20'x20', 5' deep, 75 sq ft stream.

Also on a pond this size will I need an aerator in it?

[MJK]

nevermind

http://www.pondarama.com/html/how_many_rocks.html

[tadpole]

May need an aerator or heater in the winter in case of ice-over.

[STL Ponds and Waterfalls]

Alway's get a little bigger, nothing is worse than having a low liner edge. Liner is also getting out of hand price wise so design to suit.