How Much Backing Fabric for a King Quilt
A king quilt is the largest bed size most quilters make, so the backing is where yardage really adds up. This guide works the numbers for a standard 108 by 108 inch king so you can buy the right amount of fabric the first time, whether you use wide backing or piece panels from regular cotton.
Start with the Finished King Size
The standard square king quilt finishes at 108 inches wide by 108 inches long. Some quilters build a 100 by 112 inch rectangular version for a California king mattress, but the yardage below uses the square 108 by 108 size that most backing calculators assume. Always measure your actual unfinished top before cutting, because pieced borders and seams can shift the final dimensions by an inch or two.
Add 4 Inches of Overage per Side
A backing should be larger than the top so the longarm machine or your domestic machine has room to hold and quilt the edges. The default is 4 inches per side, which turns a 108 by 108 inch quilt into a 116 by 116 inch backing requirement. Longarm quilters sometimes ask for 6 to 8 inches per side, so confirm their rule before you buy. The 116 by 116 target is what the yardage math below is built on.
Choose Your Backing Width
Yardage depends almost entirely on how wide your backing fabric is. A 108-inch wide bolt can often cover a king in a single piece, while 42-inch quilting cotton must be sewn into three panels. The table below assumes a 116 by 116 inch backing with 4 inches of overage per side.
| Fabric width | Panels | Backing yardage |
|---|---|---|
| 108" wide (single piece) | 1 | 3.5 yd (cut 116" long) |
| 90" wide | 2 | 6.5 yd (232" ÷ 36) |
| 42" quilting cotton | 3 | 10 yd (348" ÷ 36) |
Piecing 42-Inch Cotton into Three Panels
With 42-inch cotton you get about 42 inches of usable width after trimming selvages. Your required backing width is 116 inches, so 116 ÷ 42 = 2.76, which rounds up to three panels. Each panel runs the full 116-inch backing length, so three panels equal 348 inches of fabric, or 9.67 yards. Round up to 10 yards to cover shrinkage and cutting mistakes. A horizontal seam (running parallel to the quilt's long axis) is easiest to quilt and avoids tension trouble on a longarm.
Note that 108-inch wide backing saves the most work: a single 3.5-yard cut is exactly as wide as the quilt, giving about 4 inches of overage on the length but zero on the sides. If your quilter wants side overage too, you would need two wide-backing panels, which pushes yardage back up toward the pieced amount.
Frequently Asked Questions
How much backing fabric do I need for a king quilt?
A standard 108 by 108 inch king quilt needs about 3.5 yards of 108-inch wide backing cut to 116 inches long, or about 10 yards of 42-inch quilting cotton pieced into three panels. Add 4 inches of overage per side so the backing extends past the quilt edges.
Can I back a king quilt with 108-inch wide fabric?
Yes. A single 3.5-yard cut of 108-inch wide backing covers a 108 by 108 inch king in one piece. Because the fabric is exactly as wide as the quilt, you get about 4 inches of overage on the length but none on the sides, which is fine for most longarm work.
How many panels do I need if I piece king backing from 42-inch cotton?
You need three panels. The required backing width is about 116 inches and a 42-inch bolt gives roughly 42 inches of usable width after selvages, so 116 divided by 42 rounds up to three. Sew the three panels side by side and each runs the full 116-inch backing length.
How much overage should I add to a king quilt backing?
Plan for 4 inches per side as a minimum, which gives a 116 by 116 inch backing. Longarm quilters often want 6 to 8 inches per side, so check their requirements first because more overage means a wider pieced backing or a second wide-backing panel.