Quilt Backing Calculator
Backing needs to be bigger than your quilt top on every side — and pieced together if your top is wider than the fabric bolt.
Why backing needs to be bigger than the top
Both longarm quilters and home machine quilters need extra backing fabric on every edge to load the quilt onto a frame or to have wiggle room for the layers to shift slightly during quilting. 4" of overhang per side (8" total added to width and to length) is a common standard, though some longarmers ask for more.
Piecing backing from standard-width fabric
Most quilting cotton is sold around 42–44" wide, with roughly 40" usable after trimming selvages. Once your backing needs to be wider than that, this calculator assumes you'll seam multiple full-length panels side by side to reach the needed width — the standard approach for pieced backing.
Wide backing fabric skips the seam entirely
Some fabric is sold specifically as 108" wide "quilt backing" fabric, which can cover most quilt widths with no piecing at all. If you're using wide backing fabric, just divide your backing length (quilt length + overhang) by 36 for the yardage — the piecing math here doesn't apply.