Quilt Backing Calculator

Quilt backing has to be bigger than the top, and fabric off the bolt is rarely wide enough, so it gets pieced from full widths joined edge to edge. Enter the finished top size, the overhang your quilter asks for and the fabric width, and this works out how many widths to join, which direction to run the seams and the yardage to buy. Both seam directions are costed and the one that needs less cloth is the answer, with the other printed beside it. A second mode measures a piece of backing you already own against the top.

Calculator Type
Measured In
Applies to every measurement on this form and to every measurement in the answer. The geometry is all sums and ratios of lengths, so the unit cancels straight through it.

Give the finished top size and the fabric width. Both seam directions are worked out and the one that needs less cloth is the answer.

Extra backing beyond the top on all four sides. Longarm quilters usually ask for 4 in; 2 in is enough on a domestic machine. Left blank it is 4 in, or 10 cm.
Each width is listed in the unit it is actually sold in. A 44 in bolt and a 110 cm bolt are different cloth, not the same cloth converted, so both lists are here whichever unit you are working in.
Both edges together. The tight woven edge puckers a seam, so it comes off before the widths are joined. Left blank it is 1 in, or 2.5 cm.
Backing seams are usually 1/2 in and pressed open, rather than the 1/4 in used in the top. Left blank it is 1/2 in, or 1.25 cm.
Extra length if you prewash. Quilting cotton commonly loses a few per cent in the first wash.
Per yard when the measurements are in inches, per metre when they are in centimetres, matching the length the answer says to buy.
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Measured In
Applies to every measurement on this form and to every measurement in the answer. The geometry is all sums and ratios of lengths, so the unit cancels straight through it.

Measure the piece you own and this says whether it covers the top with the overhang, either way round.

Extra backing beyond the top on all four sides. Longarm quilters usually ask for 4 in; 2 in is enough on a domestic machine. Left blank it is 4 in, or 10 cm.
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