Quilt Backing Calculator
Built by Johnny Alto · free, no sign-up · updated July 26, 2026
Enter your finished quilt top size to find how much backing fabric to buy. Backing needs a few inches of overhang on every side for longarm loading and basting, and once your quilt is wider than a bolt of fabric you have to seam widths together, so the calculator picks the orientation that uses the least fabric.
Backing fabric0yards
Widths to seam0panels
Backing cut size0inches
Includes overhang on all four sides. When more than one panel is shown you seam the widths together, so add a couple of inches for the seams and always round your purchase up to the next quarter yard.
How much backing fabric does a quilt need?
Your backing has to be larger than the quilt top. Most quilters add three to four inches of overhang on every side so there is room to baste, or to load the quilt on a longarm frame. That means the backing needs to measure the top's width plus twice the overhang, by the top's length plus twice the overhang.
Quilting cotton is usually about 42 inches of usable width after you trim the selvages. As soon as your backing is wider than that, you cannot cut it in one piece, so you seam two or more widths of fabric together. The calculator works out both a vertical-seam and a horizontal-seam layout and reports whichever needs less fabric, along with the number of widths to join.
Tips before you buy
Prewash if the rest of your quilt is prewashed, since backing can shrink. Round your purchase up to the next quarter yard to leave room for squaring up, and add a couple of inches when you have seams. A pieced or wide-back fabric can avoid seaming altogether if you would rather not join panels.
Recommended gear
Quilting gear to cut and piece it
Frequently asked questions
How much backing do I need for a quilt?
Take your quilt top's width and length, add three to four inches of overhang on every side, then divide by your usable fabric width to see how many widths you seam together. The calculator turns that into total yardage.
How much overhang should quilt backing have?
Three to four inches on each side is standard, and longarm quilters often want four inches so there is room to load the quilt on the frame.
How wide is quilting fabric?
Quilting cotton is typically 42 to 44 inches wide, and about 42 inches once you remove the selvages, which is the number to use when planning seams.
Do I have to seam the backing?
Only if your backing is wider than a single width of fabric. Wide-back fabrics, sold at 108 inches, let you back most quilts without any seam.
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This calculator gives estimates for planning only; always confirm against your own measurements and species research. Some links are to our buying guides, which contain affiliate links. As an Amazon Associate I earn from qualifying purchases.
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