How to Calculate Quilt Backing
The backing is the bottom layer of your quilt sandwich, and getting the size right is the first step before you shop for fabric. Start with the finished quilt width and length, then add extra backing on every side so the longarm machine or your domestic machine has room to hold and quilt the edges.
Step 1: Add Backing Overage
A common planning default is 4 inches per side, though longarm quilters may request a specific amount. The formulas are:
- Required backing width = quilt width + (overage × 2)
- Required backing length = quilt length + (overage × 2)
Step 2: Count the Panels
Divide the required backing width by your usable fabric width (about 40 to 42 inches for 44-inch quilting cotton after trimming selvages), and round up. That gives you the number of panels you must sew together side by side.
Step 3: Convert to Yards
Multiply the panel count by the required backing length to get total inches, divide by 36, and round up to the next half or whole yard. Always buy a little extra for shrinkage and cutting mistakes.
Worked Example: a 60" × 72" Quilt
| Fabric width | Panels needed | Backing yardage |
|---|---|---|
| 42-inch usable | 2 | 4.5 yd (68" × 80" → 160" ÷ 36, rounded up) |
| 108-inch wide | 1 | 2.5 yd (single piece, 80" ÷ 36, rounded up) |
Backing Yardage at a Glance
These rounded estimates assume 4 inches of overage per side and 42-inch usable fabric, pieced horizontally:
| Quilt size | Pieced (42") | Wide (108") |
|---|---|---|
| Throw 50×60 | 3.5 yd | 1.75 yd |
| Twin 70×90 | 5.5 yd | 2.75 yd |
| Queen 90×108 | 8 yd | 3.25 yd |
| King 108×108 | 12 yd | 3.5 yd |
Frequently Asked Questions
How much backing fabric do I need for a quilt?
Add at least 4 inches of overage to each side of the finished quilt, then divide the required backing width by your usable fabric width to find the number of panels. Multiply panel count by the required backing length, divide by 36, and round up to the next half yard.
How much overage should I add to quilt backing?
A common planning default is 4 inches per side, which gives you an 8-inch margin across the width and length. Longarm quilters often request 6 to 8 inches per side, so always confirm your quilter's requirements before cutting.
How many panels do I need for quilt backing?
Panel count equals the required backing width divided by your usable fabric width, rounded up. For example, a 68-inch backing width on 42-inch usable quilting cotton needs two panels sewn side by side.
Can I use 108-inch wide backing instead of piecing panels?
Yes. Wide backing fabric (90 or 108 inches) covers most throw, twin, and queen quilts in a single piece. It costs more per yard but removes the center seam and saves significant piecing time.