Diagonal Backing Calculator

When a diagonal seam actually saves you fabric

Diagonal backing works best when your quilt is close to square and just a bit wider than one bolt width. In that situation, standard piecing forces you to buy a whole second length — mostly waste. A diagonal seam covers the extra width with significantly less yardage. This calculator compares horizontal, vertical, and diagonal layouts side by side so you can see the actual savings before you buy anything.

For very wide or very long quilts, a straight seam usually wins. Don't force a diagonal layout just because it sounds clever — run the numbers first. That's the whole point of this tool.

When you do go diagonal, starch your fabric first to minimize bias stretch along the cut line. Press the seam open since the longer seam line shows more bulk under quilting. And if you're sending the quilt to a longarm quilter, give them a heads-up about the diagonal seam — most don't mind, but it's good to ask before you cut.