Free sewing & quilting calculators
Quilt Backing Calculator
How much backing fabric to buy — with the overage your quilter needs, and the seam layout that costs the least fabric.
How quilt backing yardage is calculated
A backing has to be bigger than the quilt top on every side, because the quilt shifts as it's quilted and the edges get trimmed square afterwards. So the first step is growing the top: add your per-side overage twice to each dimension. A 60 × 80 in top with 4 in on every side needs a 68 × 88 in backing.
The second step is fitting that rectangle onto a bolt. Quilting cotton is about 44 in wide, and roughly 42 in of that is usable once the selvages come off — narrower than almost any finished quilt. So the backing gets pieced from two or three widths of fabric seamed together, and each ¼ in seam eats ½ in out of the total width, which is why two 42 in widths make 83½ in of backing rather than 84.
The last step is the one most charts skip: the seams can run either way. Cut two 88 in lengths and seam them vertically and you buy 176 in of fabric. Cut three 68 in lengths and seam them horizontally and you buy 204 in. Same quilt, nearly a yard apart. The calculator costs both and shows you the cheaper one, with the runner-up underneath.
How much extra do you need?
| 2 in per side | Quilting it yourself on a domestic machine, where you control the sandwich. |
|---|---|
| 3 in per side | A common minimum for machine quilting with a walking foot. |
| 4 in per side | The standard longarm request — the clamps and leaders need something to hold. |
| 6 in per side | Some longarm quilters ask for this on large quilts. Ask before you cut. |
If you're sending a quilt out, ask your quilter what they want before buying. Turning up with a backing that's 2 in short on each side is the single most common reason a quilt gets sent home unquilted, and it can't be fixed without adding a border to the backing.
When extra-wide backing is worth it
Backing fabric sold at 90 or 108 in wide costs more per yard, but it changes the arithmetic completely: the backing needs no seam at all, and you can turn the quilt sideways and buy the shorter dimension. That 60 × 80 in quilt needs 5 yards of 44 in cotton and about 2 yards of 108 in backing. At typical prices the wide fabric usually wins outright, and it saves you piecing and pressing a seam the length of your quilt.
A seamless back is also flatter to quilt. Seam allowances add bulk exactly where a longarm needle has to travel, and a bulky seam can distort the quilting stitches on a dense pattern.
Before you cut
Trim the selvages off every width before you piece them — selvage is woven more tightly than the rest of the fabric, and leaving it in a backing seam causes puckers that only show up after quilting, when they can't be undone. Press seams open rather than to one side to spread the bulk. If you prewash your top, prewash the backing too; cotton loses 3–5% in the first wash, and a backing that shrinks when the top doesn't will pull the finished quilt out of square. The suggested-buy figure above already includes a 5% allowance for that.