Quilt Backing Calculator
To work out quilt backing, add 4 inches to each side of your quilt top, then see how many panels of fabric cover that size. A 60 by 72 inch quilt needs a 68 by 80 inch backing: 4 1/2 yards of 42 to 44 inch fabric pieced with one seam, or 2 yards of 108 inch wide-back.
How the backing size is worked out
- Backing size: backing W = quilt W + 2 × overage, and backing L = quilt L + 2 × overage.
- Panels: panels = max(1, ceil((D − s) ÷ (U − s))). D is the side the panels must cover, U is the usable fabric width and s is the seam allowance. It is the smallest number of panels whose joined width, p × U − (p − 1) × s, reaches D.
- Vertical seams run top to bottom. Panels = panels for the backing width, and raw yards = panels × backing L ÷ 36.
- Horizontal seams run side to side. Turn the quilt a quarter turn on the fabric. Panels = panels for the backing length, and raw yards = panels × backing W ÷ 36.
- Rounding: yards round up to the next 1/8 yard. Meters = rounded yards × 0.9144, rounded up to 0.1 m.
- Tie-break: the layout with fewer yards wins. If both need the same, the one with fewer panels wins, then vertical.
- Batting should be at least as big as the backing.
The seam allowance is 0.5 in by default. A true 1/2 in seam on both pieces uses 1 in per seam, so you can set it anywhere from 0 to 1.5 in. If you only know your bed size, start with the quilt size chart.
How to calculate quilt backing
- Measure the finished quilt top, width and length.
- Add the overage to every side: 4 in, or 6 to 8 in if a longarm quilter will do the work.
- Choose the fabric width and use its usable width.
- Work out the panels needed for seams in each direction.
- Convert the length to yards by dividing inches by 36, and round up to 1/8 yard.
- Pick the layout that needs less fabric.
- Buy batting at least as large as the backing.
Worked examples
1. Standard fabric
Quilt 60 × 72, overage 4 in, 42/44 in fabric (usable 40 in), seam 0.5 in. Backing is 68 × 80 in. Vertical: panels = ceil(67.5 ÷ 39.5) = 2, raw = 2 × 80 ÷ 36 = 4.44 yd, so 4 1/2 yd (4.2 m). Horizontal: panels = ceil(79.5 ÷ 39.5) = 3, because two 40 in panels joined only reach 79.5 in. Raw = 3 × 68 ÷ 36 = 5.67 yd, so 5 3/4 yd (5.3 m). Vertical wins. Batting: at least 68 × 80 in (172.7 × 203.2 cm).
2. Wide-back fabric
Same quilt, usable width 104 in. Vertical: 1 panel, raw = 80 ÷ 36 = 2.22 yd, so 2 1/4 yd (2.1 m). Horizontal: 1 panel, raw = 68 ÷ 36 = 1.89 yd, so 2 yd (1.9 m) with no seam. Horizontal wins.
3. Longarm overage
Same quilt with 8 in overage. Backing is 76 × 88 in. Vertical: 2 panels, raw 4.89 yd, so 5 yd (4.6 m). Horizontal: 3 panels, raw 6.33 yd, so 6 3/8 yd (5.9 m). Vertical wins.
4. Queen, 90 × 108
Overage 4 in, usable 40 in. Backing is 98 × 116 in. Vertical: 3 panels, raw 9.67 yd, so 9 3/4 yd. Horizontal: 3 panels, raw 8.17 yd, so 8 1/4 yd (7.6 m). Horizontal wins.
Backing width guide
Usable width is what is left after you trim the selvages. These are conservative starting values; you can change them in the calculator.
| Fabric width | Usable width | Good for |
|---|---|---|
| 42 to 44 in | 40 in | Standard quilting cotton; small and medium quilts |
| 54 in | 50 in | Home-decor weight fabric |
| 60 in | 56 in | Flannel and some apparel fabrics |
| 108 in wide-back | 104 in | Large quilts with no seam |
How to piece a quilt backing
- Cut each panel to the backing length.
- Trim off the selvages.
- Sew the panels together with a 1/2 in seam.
- Press the seam open so it lies flat for quilting.
- Check that the joined piece is at least as big as the backing size, then trim if needed.
Wide-back fabric note
Wide-back fabric is quilting cotton sold in an extra-wide width, commonly 108 inches. It lets you back a large quilt with no seam. It is cut by the yard like any other fabric. After the selvages are trimmed, plan on about 104 inches of usable width, which is the default here. Some makers sell 106 inch widths; type your own number in the usable width box if yours differs.
Frequently asked questions
How big should the backing be on a quilt?
Make the backing at least 4 inches larger than the quilt top on every side, which means 8 inches added to both width and length. Many longarm quilters ask for 6 to 8 inches per side. Extra backing is trimmed after quilting, while backing that is too small causes real trouble, so measure the finished top first.
How much backing do you need for a 3 yard quilt?
It depends on what "3 yard" means. For a quilt about 3 yards (108 inches) square, the backing is 116 by 116 inches with 4 inches of overage. That takes 6 1/2 yards of 108 inch wide-back fabric, or 9 3/4 yards of 42 to 44 inch fabric pieced with two seams. Enter your own size above for an exact answer.
How much backing do I need for a quilt?
Add 8 inches to the width and length of your quilt top, then see how many fabric widths it takes to cover that size. A 60 by 72 inch quilt needs a 68 by 80 inch backing, which is 4 1/2 yards of standard 42 to 44 inch cotton or 2 yards of 108 inch wide-back. The calculator compares both seam directions.
How many yards of 108 fabric for quilt backing?
If the shorter side of your backing is 104 inches or less, one length of 108 inch wide-back fabric covers it, so the yardage is the other side divided by 36, rounded up. For a 60 by 72 inch quilt that is 2 yards, with the fabric turned sideways. Larger quilts may need two pieces.
How do you piece a quilt backing?
Cut the panels to your backing length, trim off the selvages, and sew them together with a 1/2 inch seam. Press the seam open so it lies flat for quilting. Check that the joined piece is at least as big as your backing size, then trim. Either seam direction works; the calculator suggests the one that uses less fabric.
What is wide back quilt fabric?
Wide-back fabric is quilting cotton sold in an extra-wide width, commonly 108 inches, so a large quilt can be backed with no seam. It is cut by the yard like any other fabric. Its usable width is a little less than the label after the selvages are trimmed, about 104 inches, which is the default in our calculator.