I do longarm quilting and ask that the backing and batting be at least 4 inches larger on all sides, so one would add 8 inches to the length and width. There are good reasons for this. When the quilt backing is loaded onto the longarm they are either pinned or clamped onto the leaders requiring extra fabric. The batting rests on the top of the backing and then the quilt top rests on the batting. Longarmers need this extra fabric for attaching the backing and also they baste the sides and top and bottom of the quilt top to the backing and batting before quilting. They also quilt off the sides of the quilt top to ensure that the quilting will be secured when the binding is attached. Clear as mud, then there are many YT videos that show how longarmers load quilts. It is interesting to watch this process. It will give one an appreciation for their longarm quilter. I realize there is cost involved but it is truly a work of heart to finish quilts for others.