Thimblewise

Quilt Backing Calculator

Enter your quilt top size to see how much backing fabric to buy, how many panels to sew together, and which seam direction wastes the least.

4" is the usual longarm request.
Usable width after trimming selvages.

How the backing math works

The backing has to be bigger than the quilt top so the quilting frame (or your hands) can hold it taut, and so it doesn't come up short if the layers shift.

  1. Add the overhang. Backing width = top width + 2 × overhang. Backing length = top length + 2 × overhang.
  2. Count the panels. If the backing is wider than your fabric, you sew lengths of fabric side by side. Each seam uses ½" (¼" from each panel), so n panels cover n × fabric width − (n − 1) × ½".
  3. Multiply by panel length. Total inches = panels × the length of each panel. Divide by 36 for yards and round up to the next ⅛ yard, which is what most shops cut.
  4. Try both directions. Turning the seams sideways changes the panel count and length. Whichever total is smaller is the better buy.

Example: a 60" × 80" quilt with 4" overhang needs a 68" × 88" backing. With 40" usable fabric, vertical seams need 2 panels of 88" = 176" = 5 yards. Horizontal seams need 3 panels of 68" = 204" = 5¾ yards. Buy 5 yards and sew one vertical seam.

Backing yardage chart

Common quilt sizes with 4" overhang per side and 40" usable fabric width. Wide backing assumes 106" usable.

QuiltTop sizeStandard fabric108" wide backing
Baby36" × 52"2½ yd (2 horizontal panels)1¼ yd
Throw60" × 70"3⅞ yd (2 horizontal panels)2 yd
Twin70" × 90"5½ yd (2 vertical panels)2¼ yd
Full84" × 90"7¾ yd (3 horizontal panels)2⅝ yd
Queen90" × 100"8¼ yd (3 horizontal panels)3 yd
King108" × 100"9 yd (3 vertical panels)6 yd (2 panels)

Tips for a smoother backing

Questions quilters ask

How much bigger than the quilt top should the backing be?

Most longarm quilters ask for 4 inches extra on every side, so 8 inches added to both the width and the length. If you quilt on a domestic machine, 2 to 3 inches per side is usually enough. Check with your longarmer before you buy.

Should backing seams run vertically or horizontally?

Either works structurally. Choose whichever uses less fabric for your size; this calculator shows both. Many longarmers prefer horizontal seams because the seam lies parallel to the rollers, but vertical seams are fine on most frames.

Do I need to prewash backing fabric?

Quilting cotton can shrink 2 to 5 percent. If you prewash, buy roughly 5 percent more than the calculated yardage, or about an extra quarter yard on a queen-size backing.

Is wide backing cheaper than piecing standard fabric?

Often, for anything throw-size or larger. A 108-inch wide backing covers most queen quilts with no seams and usually needs less than half the yardage, though it costs more per yard. Compare total price, not price per yard.