Use the free tool below: your data never leaves your browser — all work happens on your device, and nothing is uploaded to any server.
Why Quilt Backing Needs Its Own Calculation
The backing is the fabric on the back of a quilt. It must be larger than the quilt top, because the quilting process shifts layers slightly, and the long-arm quilter or your own machine needs extra fabric to hold. A backing that is exactly the size of the top will almost always come up short at an edge, and a short backing cannot be fixed after quilting starts.
Backing fabric also comes in limited widths. Standard quilting cotton is about 110 cm wide, while wide backing fabric is about 280 cm. A quilt wider than your fabric needs joined pieces, and those joins change how much fabric to buy. This calculator handles both problems: the extra overhang and the joining.
How This Calculator Works
It starts by adding your overhang to each side of the quilt top. Ten centimetres per side is a common recommendation, giving twenty centimetres extra in each direction. That gives the backing size you actually need. Then it divides the needed width by your backing fabric width and rounds up, to find how many lengths must be joined side by side. Multiply the piece count by the needed length, and you have the total backing length to buy.
Seams are part of the plan, not an afterthought. When two backing lengths are joined, the seam itself uses a little width, and the pieces should be cut slightly generous so the seam can be pressed and the backing stays square. The overhang covers this, which is another reason not to set it to zero.
How to Use It
Enter your quilt top length and width, the width of your backing fabric, and the overhang you want on each side, in centimetres or inches. Ten centimetres is a safe default. Press Calculate. You get the backing size needed, the number of pieces to join, and the total length to buy, in your unit plus metres and yards.
If the calculator says two pieces, plan the join. Many quilters put the join off-centre so it does not run down the middle of the quilt back, and they press the seam open for a flat finish. If you use a directional print for the backing, make sure all pieces run the same way before cutting.
Worked Example
A quilt top 200 cm by 160 cm, with 10 cm overhang per side and backing fabric 110 cm wide, needs a backing of 220 cm by 180 cm. The width, 180 cm, divided by 110 cm, rounds up to 2 pieces. Two pieces at 220 cm each give a total of 440 cm, or 4.4 metres, of backing fabric.
Compare that with wide backing fabric at 280 cm. The needed width of 180 cm fits in one width, so only one piece of 220 cm is needed, or 2.2 metres. Wide backing costs more per metre but uses far less length, and it has no centre seam, so it is often the better choice for large quilts.
Tips for Backing
Pre-wash backing fabric if you pre-washed the top fabrics, so all layers shrink together. If the top is not pre-washed, do not pre-wash the backing either, or the layers will behave differently in the first wash. Press the backing well and square it up before quilting; wrinkles and skew in the backing show as puckers on the finished quilt.
Save large backing offcuts. They make excellent tote bags, cushion backs, and test pieces for quilting tension. Backing fabric is usually plain or simply patterned, which makes it very useful for practice.
Common Mistakes
The most expensive mistake is buying backing exactly the size of the top. Quilting shifts layers, and even a careful quilter needs grip fabric beyond the top edge. Always include overhang. Another mistake is forgetting that joined pieces need seam allowances: two pieces cut exactly to the needed width will be slightly short after seaming, so the overhang must absorb that too.
A third mistake is buying backing before the top is finished. Quilt tops often grow or shrink slightly during piecing. Measure the finished top, then buy the backing.
Frequently Asked Questions
How much overhang is enough? Ten centimetres per side is standard for home quilting. Long-arm quilters often ask for ten to fifteen centimetres, so check with yours before buying.
Can I piece the backing from scraps? Yes, many quilters piece creative backs from leftover fabric. Just make sure the pieced back is at least as large as the needed size, and press all seams flat.
Is wide backing worth it? For quilts wider than about 150 cm, usually yes. It avoids a long centre seam and often uses less total fabric.
Please note: sewing results here are estimates and guidance only. Fabric, pattern and personal ease vary, so measure twice and buy a little extra.
Related calculators
- Spanish version
- Quilt Block Calculator – Blocks per Row, Rows and Total Blocks
- Serger Thread Calculator – Thread Use by Overlock Stitch Type