Quilt Backing Calculator
Enter the finished quilt top size, the extra your quilter asks for on each side, and the fabric width. The calculator works out how many panels to sew together and which seam direction uses less fabric.
The formula
Worked example. a 60 × 80 in top with 4 in extra needs a 68 × 88 in back; on 42 in fabric that is two lengthwise panels, 176 in, so buy 5 yd.
How to use it
- Measure the finished quilt top, including borders.
- Enter the extra backing needed on each side. Longarm quilters usually ask for 4 in (10 cm); for hand or domestic-machine quilting, 2–3 in is common.
- Enter the usable width of your backing fabric: about 42 in (107 cm) for quilting cotton after trimming selvages, or 108 in (274 cm) for wide-back fabric.
- Buy the amount shown. The seam allowance is the width each panel loses where panels are sewn together.
Questions
Should the backing seam run lengthwise or crosswise?
Either works structurally. Lengthwise seams are the usual choice for larger quilts; crosswise seams often save fabric on wide, short quilts. The calculator shows both so you can choose.
Why do longarm quilters need extra backing?
The backing is clamped to the frame rollers and side clamps, and the quilt top can shift slightly as it is stitched. 4 in on every side gives room for both.
Is wide-back fabric worth it?
For large quilts, usually. A single 108 in piece avoids piecing and often needs less length than two or three panels of standard cotton.