Hi there! I’m so glad you’re enjoying our tutorials! If it were me, I would try a piece that’s maybe 14″ by 12″. 14″ would be the length of the bag and 12″ would get folded in half. Maybe just try with a cheap piece of muslin and baste the side and bottom and see if you need more room. You also might want to check out this tutorial: https://www.professorpincushion.com/professorpincushion/produce-bag/ It’s a produce bag but it has a drawstring top so you can work it out for your own shoe bag to keep them from falling out. Hope that helps!