Must Be At Least 12" larger than your top.
If your top measures 80X80 your back must be at least 92X92 and squared. Backing can be larger than the requested 12" but no less than that. Please note that I can not accept the wide painted-on print fabric or glitter for the backing. It is usually a white on white or white on cream that is mostly sold at Joanne's, Hobby Lobby, or Hancocks. I do sell 108" backing starting at $18/yd if you should need it. I have several to choose from. Please be sure to prewash, press, and square your backing.
Batting Should be at least 3" larger than your top.
I have Quilters Dream batting available here for purchase. Other batting brands that work are Hobbs, Warm and Natural, and Pellon. The Mountain Mist and Fairfield brands of batting do not work well so I no longer accept them.