About this tool
Quilt Backing & Batting Calculator tells you how much backing fabric and batting a quilt needs. Enter the finished quilt-top width and length, your backing fabric's usable width (often 42–44 inches, or a wide 108-inch bolt), and how much the backing should extend past the top on each side. It returns the yardage to buy, the number of fabric widths to seam, and the batting size.
The backing must be larger than the top, so needed width = quilt width + 2 × overage and needed length = quilt length + 2 × overage, using about 4 inches of overage per side by default. Panels = ceil(needed width ÷ fabric width) is how many widths you seam side by side, and yardage = panels × needed length ÷ 36, rounded up to the nearest eighth of a yard. Batting matches the needed width × needed length.
The 4-inch overage gives the longarm or your basting room to spare and covers any shifting during quilting; trim it back after finishing. If your quilt is wider than a single fabric width, you will seam two or more panels — turning the pieced backing so the seam runs horizontally often saves fabric.