I am replacing the elastic on 3 king sized fitted sheets for a friend. What I need to know and cannot find anywhere is how much elastic do I need to thread through the casing? All of the elastic is worn and stretched out. I am bleary eyed from searching on google for this information. I need to put this elastic ALL THE WAY AROUND THE SHEETS. NOT JUST THE CORNERS. The woman I am doing this for wants the sheets that way and to be honest, all of my sheets are that way as well. I have never seen them just in the corners. Does anyone know how much elastic I would need to thread through the casings for king sized fitted sheets?