A few useful things to know
How to use this backing calculator
A quilt back needs room beyond the quilt top. Enter your finished top size and the usable width of your fabric. We compare two balanced-panel layouts and keep every seam allowance in the calculation.
- Measure the whole quilt top, including any borders.
- Add the overhang your quilting service requires on every side. Four inches is a starting point, not a universal longarm requirement.
- Measure between the selvedges after removing them. A bolt sold as 44 inches may provide only 42 usable inches.
- Review the two seam directions, then copy the shopping list or download the cutting plan.
A worked example
For a 60 × 80 inch quilt, 4 inches of overhang, 42 inches of usable fabric and ½ inch seams, the backing must cover 68 × 88 inches. Cut two panels at least 34½ × 88 inches for vertical seams: 176 inches off the bolt, or 4.889 yards. Rounded up to an eighth, buy 5 yards. Horizontal seams need three 68-inch lengths: 204 inches, rounded to 5¾ yards.
The method behind the result
Required backing = quilt size + twice the overhang. For a joined width B, usable bolt width F and seam allowance s, the smallest panel count is ceil((B − 2s) / (F − 2s)). Every join consumes 2s. Yardage is the sum of panel cut lengths, plus any separate matching reserve.
What this plan assumes
Panels are balanced in width, all cut from one fabric, with ordinary straight seams pressed open. The least fabric result is selected among the two supported regular-panel layouts. Scraps, inset strips and diagonal piecing are outside this comparison. Fabric width means usable width after selvedges; shrinkage and squaring-up fabric are not automatically included.
Common mistakes to avoid
- Entering the bolt label width instead of the usable fabric width.
- Adding overhang only once rather than on both sides.
- Buying for a two-panel join without subtracting the seam loss.
- Choosing a cheaper layout that turns an upright print sideways.