Quilt backing calculator

How it works

First the calculator adds the extra to every side of your quilt top. Then it works out how many widths of fabric, sewn together, are needed to cover the backing, and tries it both ways:

• Vertical seams: panels run the length of the quilt, side by side, to cover its width.
• Horizontal seams: panels run across the quilt, stacked, to cover its length.

backing size = quilt size + 2 × extra
panels = enough fabric widths to cover the backing, allowing for seams
fabric = panels × panel length, rounded up to the next ⅛ yd

Example: a 60 × 80 in quilt with 4 in extra needs a 68 × 88 in backing. Two panels of 88 in with a vertical seam cover it, which is 176 in or 5 yd of 42–44 in fabric. Horizontal seams would need three panels of 68 in, 204 in in total, so vertical wins.

Tips

• Prewashing? Cotton can shrink a few percent. Buy a little extra, or wash before measuring.
• Directional prints may force one seam direction. Check the pattern runs the way you want before picking the cheaper layout.
• Press backing seams open to reduce bulk, and use a slightly shorter stitch for strength.
• Leftover width from the last panel is handy for a label, a hanging sleeve or scrappy binding.