Quilt backing calculator
Enter your quilt size and this tool tells you how much backing fabric to buy, and the piecing layout that wastes the least.
Enter your numbers
How it is calculated
The backing must be larger than the quilt top, because layers shift during quilting and a longarm frame needs fabric to grip. So the backing size is your quilt size plus an overhang on every side (4 in per side for home quilting, 8 in for most longarm services).
Quilting fabric is narrower than most quilts, so the backing is usually pieced from two or three panels. The tool compares every layout: a single panel, a railroaded single panel, panels joined with vertical seams, and panels joined with horizontal seams. It picks whichever uses the least fabric, then rounds up to the next quarter yard.
Worked example
A 60 x 70 in throw quilt with 4 in overhang needs a 68 x 78 in backing. From standard 42 in quilting cotton (40 in usable), two panels joined with one horizontal seam use 2 x 68 = 136 running inches, which is 3.78 yards. The vertical layout would use 156 inches, so horizontal wins. Buy 4 yards, or about 3.5 meters.
Common questions
- How much bigger than the quilt should the backing be?
- At least 4 inches on every side for quilting on a home machine, so 8 inches added to both the width and the length. If a longarm quilter will finish it, ask them; most request 8 inches per side.
- How many yards of backing do I need for a queen quilt?
- A typical 90 x 95 in queen quilt with 4 in overhang needs a 98 x 103 in backing. From 42 in quilting cotton that is three panels, roughly 8 to 8.5 yards. From 108 in wide backing fabric it is a single seam-free piece of about 2.875 yards. Run your exact size through the calculator above.
- Should backing seams run vertically or horizontally?
- Whichever direction uses less fabric, which depends on your quilt's proportions. The calculator compares both. Horizontal seams are fine for most quilts; some longarm quilters prefer them because the seam loads onto the frame with less bulk.
- Is wide back fabric worth it?
- Usually yes for anything bigger than a throw. 108 in wide backing avoids seams entirely and often costs less per square inch than piecing regular yardage. Choose the wide back option in the fabric width menu to compare.
- Do I need extra if I prewash my fabric?
- Yes. Quilting cotton can shrink 3 to 5 percent, so add about 10 percent to the amount you buy if you prewash.
Related tools
SewCalc results are careful estimates based on standard practice. Fabrics, brands and personal technique vary, so always confirm measurements against your own pattern or project before cutting.