When I do back to front binding, I leave the backing fabric 1' larger, turn under 1'4" and bring it to the front and top stitch it down. If it is a large quilt, I probably would leave it 1 1/4" larger as I like a wider binding on bigger quilts.The width also depends on the batting you've used as a thicker batting will require a little more fabric to turn over the edge. A decorative stitch also looks good on these bindings.