Quilt CalculatorHow much backing fabric do I need?
Add 4 inches to each side of the quilt top to get the backing size. Divide the backing width by the usable fabric width to get the number of panels. Multiply panels by the backing length, then divide by 36 for yards. Try both seam directions and buy the smaller total.
The back of a quilt has to be bigger than the top. The extra lets you square up the quilt. On a longarm frame it also gives the clamps something to hold. One quilter's prep sheet asks for 4 inches per side on baby and throw quilts and 5 inches on twin and up (Midge's Stitches).
The backing formula
Backing width = quilt width + 2 x extra
Backing length = quilt length + 2 x extra
Panels = (side to cover minus 1) / (usable width minus 1), rounded up
Yards = panels x panel length / 36
The "minus 1" counts the seam. A 1/2 inch seam uses 1 inch of fabric for each join. For vertical seams, the side to cover is the backing width and each panel is as long as the backing. For horizontal seams, flip it.
Worked example: a 60 by 80 inch quilt
- Backing size: 60 + 8 = 68 wide, 80 + 8 = 88 long.
- Vertical: 68 is wider than 40, so you need 2 panels, each 88 inches long. That is 176 inches, or 5 yards after rounding up.
- Horizontal: 88 needs 3 panels, each 68 inches long. That is 204 inches, or 5 3/4 yards.
- Buy 5 yards and sew 2 panels side by side.
Vertical vs horizontal seams
Vertical seams run from the top of the quilt to the bottom. Horizontal seams run side to side. Neither is stronger. The best choice is the one that wastes less fabric, and that depends on the size of the quilt and the width of your fabric.
As a rule of thumb, horizontal seams often win on throws and lap quilts. Vertical seams often win on long bed quilts. Some longarm quilters prefer seams that run parallel to the rollers. Ask before you sew.
Backing yardage chart
This chart uses 4 extra inches per side and 40 inches of usable width. The last column is for 108 inch wide backing with 106 usable inches. All values round up to the next 1/8 yard.
| Quilt top (in) | Backing (in) | Vertical | Horizontal | 108 in wide |
|---|---|---|---|---|
| 36 x 52 | 44 x 60 | 3 3/8 yd | 2 1/2 yd | 1 1/4 yd |
| 50 x 65 | 58 x 73 | 4 1/8 yd | 3 1/4 yd | 1 5/8 yd |
| 60 x 80 | 68 x 88 | 5 yd | 5 3/4 yd | 2 yd |
| 70 x 90 | 78 x 98 | 5 1/2 yd | 6 1/2 yd | 2 1/4 yd |
| 84 x 102 | 92 x 110 | 9 1/4 yd | 7 3/4 yd | 3 1/8 yd |
| 90 x 108 | 98 x 116 | 9 3/4 yd | 8 1/4 yd | 3 1/4 yd |
| 108 x 108 | 116 x 116 | 9 3/4 yd | 9 3/4 yd | 6 1/2 yd |
Bold marks the cheaper layout for 40 inch fabric.
Using 108 inch wide backing
Wide back fabric comes on bolts about 108 inches across. Most bed quilts fit on one piece with no seam. Run the wide side across the quilt, then buy enough length to cover the backing length. A 98 by 116 inch queen back takes 116 inches, which is 3 1/4 yards. The same back from 40 inch cotton takes 8 1/4 yards. Pick "108 in wide back" in the tool to see your number.
How to sew a pieced backing
- Cut each panel to the length the tool shows.
- Cut off the selvages along the edges you will join. Selvages are tight and can pucker.
- Pin panels right sides together and sew with a 1/2 inch seam.
- Press the seam open to cut down bulk.
- Trim the last panel if the tool lists extra width. Check that the back is bigger than the top on all four sides.
Other quilt calculators
- Binding strips and yards
- Quilt size chart for every bed
- Batting size and yards
- Border fabric yardage
FAQ
How much bigger should the backing be than the quilt top?
Most quilters add 4 inches on every side, so the back is 8 inches wider and 8 inches longer than the top. Some longarm quilters ask for 5 inches per side on twin size and larger quilts. Ask your quilter before you buy fabric.
How many yards of backing do I need for a queen quilt?
A 90 by 108 inch queen top with 4 extra inches per side needs a 98 by 116 inch back. With 40 inches of usable width that is 3 panels of 98 inches, or 8 1/4 yards. With 108 inch wide backing it is 3 1/4 yards.
Should backing seams run vertical or horizontal?
Pick the layout that uses less fabric. The tool shows both. Vertical seams run the long way and often suit tall quilts. Horizontal seams run across and often save fabric on throws. Seam direction does not change how the quilt wears.
What does usable width mean?
Usable width is the fabric width after you cut off the selvages. A 42 to 44 inch bolt of quilting cotton often gives about 40 to 42 inches you can use. Measure your own fabric, then type that number in the custom box.
When is 108 inch wide backing worth it?
Wide backing lets most bed quilts use one piece with no seams. For quilts wider than about 70 inches it often needs far fewer yards than standard cotton. Compare the two totals in the tool before you shop.
Why does the tool round up to the next 1/8 yard?
Shops cut fabric in steps of 1/8 yard or larger. Rounding up makes sure you never buy too little. If your shop cuts in 1/4 yards, round up again.