How Much Backing Fabric Do I Need?

The backing is the largest single piece of fabric in most quilts, so getting the yardage right matters. The two decisions are how much extra to allow around the edges and which direction to run the seams.

Step 1: add overhang on every side

The backing must be bigger than the quilt top. Fabric draws up as it is quilted, and longarm frames need extra fabric to clamp. Most longarm quilters ask for at least 4 inches on every side, which means adding 8 inches to both the width and the length. If someone else is quilting for you, ask what they need before you buy: some ask for more.

Step 2: decide how many fabric widths you need

Standard quilting cotton has about 42 inches of usable width, so anything wider than that needs two or more lengths sewn together. You can run those seams down the length of the quilt (vertical) or across it (horizontal). The fabric needed can be very different, so it is worth checking both.

Vertical seams: panels needed = backing width / 42, rounded up. Each panel is as long as the backing length.
Horizontal seams: panels needed = backing length / 42, rounded up. Each panel is as long as the backing width.

Multiply the number of panels by the panel length to get inches of fabric, divide by 36 and round up to the next 1/8 yard.

Worked example: a 60 x 72 inch throw

Backing size: 68 x 80 inches.
Vertical seams: 68 / 42 rounds up to 2 panels, each 80 inches long: 160 inches, or 4 1/2 yards.
Horizontal seams: 80 / 42 rounds up to 2 panels, each 68 inches long: 136 inches, or 3 7/8 yards.

Running the seam across the quilt saves 5/8 yard here.

Worked example: a 90 x 108 inch queen

Backing size: 98 x 116 inches.
Vertical seams: 3 panels of 116 inches: 348 inches, or 9 3/4 yards.
Horizontal seams: 3 panels of 98 inches: 294 inches, or 8 1/4 yards.
With 108 inch wide-back (about 106 inches usable): one panel 116 inches long with no seam, or 3 1/4 yards.

For large quilts, wide-back fabric often means less cutting and no seams to line up. Compare the price per yard against the yardage before you decide.

Tips for a smooth backing

Trim selvages before seaming; they shrink differently from the rest of the fabric.
Press the backing seams open to reduce bulk.
Pre-wash or not, treat the backing the same way as the top.
Mark the top edge of a directional print so it isn't loaded sideways.

Frequently asked questions

Can I piece the backing from leftover fabric?

Yes. A pieced backing uses up stash and can be a design feature. Make sure the finished backing is still at least the size worked out above, keep seams pressed flat, and avoid placing a seam exactly where the quilt will fold most often.

Why does my shop's chart give a different number?

Charts often assume a different overhang, a different usable width or a single seam direction. The method above shows each assumption, so you can change any of them to match your situation.

Does the backing need to be pre-washed?

Not necessarily, but treat the backing the same way as the top. If one is pre-washed and the other isn't, they can shrink by different amounts the first time the quilt is washed, which can cause puckering.

What about the batting?

Batting should be about the same size as the backing, or a little smaller, so it also needs the overhang. Batting is often sold in packaged sizes; choose the next size up from your backing measurements.

Try the calculator

The quilt backing calculator compares both seam directions and wide-back fabric for any size and overhang. The Quilt Planner includes a backing worksheet with the same steps, so the numbers stay with the project.

Related tool: open the calculator.