How much fabric do I need for a quilt backing?

The short answer: make the backing about 8 inches wider and 8 inches longer than your quilt top (4 inches on each side), then work out how many widths of fabric that takes and add them up.

Here is how to do it step by step.

Start with the backing size

Take your finished quilt top and add the overhang on all four sides. Four inches per side is the common amount; if a longarm quilter is finishing it, ask them, because many want 4 to 6 inches per side.

For a 60 by 80 inch quilt with a 4 inch overhang:

• Backing width: 60 + 4 + 4 = 68 inches
• Backing length: 80 + 4 + 4 = 88 inches

Decide how many widths of fabric you need

Quilting cotton is usually about 42 inches wide off the bolt, and closer to 40 inches once you trim the selvages. If your backing is wider than that (68 inches is), you need to seam two or more widths together.

• 68 inches of width divided by 40 usable inches rounds up to 2 widths.
• Each width needs to be 88 inches long.
• So you buy 2 times 88 inches = 176 inches, which is about 5 yards.

Seam direction matters

You can run the seams vertically (widths side by side) or horizontally (widths stacked). One direction almost always uses less fabric than the other. For a tall, narrow quilt, vertical seams usually win; for a wide, short quilt, horizontal seams can win. It is worth checking both.

Quilt	Backing	Widths	Yardage
60 x 80	68 x 88	2	about 5 yd
90 x 90	98 x 98	3	about 8.25 yd
40 x 50	48 x 58	2	about 2.75 yd

Let the app do it

The quilt backing calculator does all of this instantly and picks the seam direction that wastes the least fabric. Sashing on iPhone does the same offline, and remembers your usual overhang so you never re-enter it.