Quilt Backing Calculator
Work out how much backing fabric a quilt needs — including overhang for quilting — and the most economical seam direction.
How it works: Backing must cover the quilt plus overhang on all sides (longarm quilters usually want 3–4 in). We compare seaming panels vertically vs. horizontally and recommend whichever uses less fabric.
This calculator finds how much backing fabric a quilt needs, including an overhang on each side for quilting, and it compares the two ways of joining the fabric. The backing is the quilt size plus the overhang on both sides. A 60 by 80 inch quilt with a 4 inch overhang needs a backing of 68 by 88 inches.
Seams can run along the length or across the width. With 42 inch fabric, running the seam down the length needs two panels of 88 inches, which is 176 inches, or about 4.9 yards. Running across needs three panels of 68 inches, which is 204 inches, or about 5.7 yards, so the lengthwise seam is more economical here.
Wide backing fabric, 90 to 108 inches, can avoid seams altogether and is often worth the cost. Trim the selvages before you sew, and press the seam open so the quilting passes smoothly over it.
A larger overhang gives more room if the layers shift as you quilt, which is helpful for large quilts and for beginners. Wash the backing first if you wash the top, so that both shrink the same amount.