Getting the fabric sums right
Three separate calculations trip quilters up at the fabric shop, and all three are easy once you see them written down. Binding is about the perimeter; backing and batting are about the area plus an overhang.
Binding
Measure right around the quilt — that's twice the width plus twice the length — then add about ten inches for turning the corners and joining the strip ends on the diagonal. Divide by your usable fabric width to find how many strips to cut, always rounding up. Multiply the number of strips by the strip width to see how many inches of fabric to buy, and divide by 36 for yards.
Buy the next quarter yard up. Binding is the last thing you do on a quilt that has taken weeks, and being three inches short at that point is genuinely miserable. An extra quarter yard costs very little and often becomes the label or a scrappy border on the next project.
Backing
Your backing needs to be bigger than the quilt top on every side — two inches if you're quilting it yourself on a domestic machine, and four inches if you're sending it to a longarm quilter, who needs something to clamp. Always ask your quilter what they want before cutting.
Standard quilting cotton is only about 40 usable inches wide, so anything larger than a lap quilt needs the backing seamed from two or three panels. The calculator works out which direction to seam and how many yards that takes. Extra-wide backing fabric at 108 inches avoids seaming altogether — it costs more per yard but you buy far fewer of them, and it saves an evening of pressing long seams.
Batting
Batting is sold both by the yard from a roll and in pre-cut packages named after bed sizes. The pre-cut packages are usually the better value if your quilt fits inside one, so the calculator tells you which package size to reach for. Do check the actual measurements on the packet, as they vary a little between brands.
Pressing and prewashing
Whether to prewash is one of quilting's great debates and there is no single right answer. What matters for these sums is consistency: if you prewash one fabric, prewash them all, and remember that cotton can shrink by 3 to 5%, so buy a little extra if you plan to wash before cutting.
Questions we're often asked
How much binding do I need for a quilt?
Measure the perimeter — twice the width plus twice the length — and add about ten inches for corners and joins. For a 60 × 80 inch quilt that's 290 inches, which needs eight strips cut at 2½ inches across a 40 inch fabric width, or roughly ⅝ of a yard.
What width should I cut binding strips?
2½ inches is the standard for double-fold binding on a normal quilt, giving a finished binding of about ⅜ inch. Cut 2¼ inches for a narrower look, or 2¾ to 3 inches if your batting is thick and lofty.
How much bigger should the backing be?
Two inches larger on each side if you are quilting it yourself, and four inches if a longarm quilter is doing it — they need extra to load the quilt onto the frame. Always ask your quilter first, as some prefer six.
Should I use wide backing fabric?
For anything bigger than a lap quilt it is worth pricing up. Extra-wide backing at 108 inches costs more per yard, but you need far less of it and you avoid seaming entirely, which saves both fabric and a good deal of pressing.
How do I join binding strips?
Join them on the diagonal rather than straight across. Lay two strip ends at right angles, right sides together, sew corner to corner, trim the excess and press the seam open. The bulk is then spread across the width instead of forming a lump.