How Much Fabric for Quilt Backing and Binding (With Easy Math)

Most patterns list fabric for the quilt top, but backing and binding are often left to you. The math is simple once you know three numbers: the size of your finished top, how wide your fabric is, and how much extra to allow.

What you need to know first

• Quilt size: measure your finished top across the middle in both directions.
• Usable fabric width: standard quilting cotton is about 42 to 44 inches wide. Plan on about 40 inches usable after trimming selvages and shrinkage.
• Extra allowance: add 4 inches to every side of the backing (8 inches to each measurement). If a longarm quilter is finishing your quilt, check with them, as many ask for 4 to 6 inches per side.

Backing: the formula

1. Add 8 inches to the quilt's width and length.
2. Divide the backing width by 40 and round up. That's how many lengths (panels) of fabric you need to sew together.
3. Multiply the number of panels by the backing length, then divide by 36 to get yards. Round up to the next quarter yard.

Example: a 60 × 72 inch throw quilt needs a backing about 68 × 80 inches. 68 ÷ 40 = 1.7, so you need 2 panels. 2 × 80 = 160 inches, and 160 ÷ 36 = 4.4, so buy 4½ yards.

Tip: Sometimes running the seam the other way saves fabric. Try the math with the quilt's width and length swapped and buy whichever comes out less. Longarmers prefer horizontal seams on their backing.

Wide backing

Wide backing fabric comes in widths of about 108 inches, so most quilts need just one piece and no seams. Buy the backing length (quilt length plus 8 inches) in yards. For the 60 × 72 throw above, that's 80 inches, or 2¼ yards of wide backing.

Binding: the formula

1. Add up all four sides of the quilt (the perimeter), then add 12 inches for corners and joining.
2. Divide by 40 and round up. That's how many strips to cut across the width of the fabric.
3. Multiply the number of strips by your strip width (2½ inches is the most common), then divide by 36 for yards. Add a little extra to be safe.

Example: the 60 × 72 throw has a perimeter of 264 inches. 264 + 12 = 276, and 276 ÷ 40 = 6.9, so cut 7 strips. 7 × 2½ = 17½ inches, about ½ yard. Buy ⅝ yard to allow for straightening the edge.

Pick the backing and binding with the top

The binding is a thin frame around the whole quilt, and it changes the look more than you'd expect: a dark binding defines the edge, while one matching the border lets the quilt fade out softly. With Quilt Preview you can see your finished quilt in your own fabric and try different choices before you cut, so the backing and binding are part of the plan from the start rather than an afterthought.