How this calculator works
Binding goes all the way around the quilt, so its length starts as the perimeter: twice the width plus twice the length. Add an allowance for the four corners, where the binding turns, and for the final join. The strips are cut across the fabric, so the number of strips is the binding length divided by the usable fabric width, rounded up. Each strip is as wide as the binding you want; the fabric length to buy is the strip count multiplied by that width. Bias binding is cut on the diagonal, which wastes more at the ends, so the calculator adds 15 percent to the length.
Formula
perimeter = 2 x (quilt width + quilt length). binding length = (perimeter + corner allowance) x 1.15 for bias, or x 1 for straight. strips = binding length / fabric width, rounded up. fabric length = strips x strip width.
Worked example
A 150 by 200 cm quilt has a perimeter of 700 cm. With a 25 cm allowance the binding length is 725 cm. On 110 cm fabric that is 7 strips, rounded up from 6.59. At 5.72 cm wide each, the fabric length is 40 cm, or 0.4 m. For bias tape the length becomes 833.75 cm, which is 8 strips and 46 cm.
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Frequently asked questions
How wide should quilt binding be?
A common finished binding is 1/4 inch on each side of the quilt, which takes a strip about 2.25 inches or 5.7 cm wide. Wider binding gives a heavier edge; narrower binding takes a smaller strip. Check the pattern before cutting.
Why add 25 cm for the corners?
Each mitred corner needs a little extra fabric to turn cleanly, and the start and end must overlap to join. Twenty-five centimetres is a practical allowance for a bed quilt. Add more for very thick batting or a narrow strip.
When should I use bias binding?
Bias binding stretches around curves and is the right choice for a quilt with curved edges. On straight edges, straight-grain binding is stronger and uses less fabric. The 15 percent allowance here covers the diagonal joins, not a full cutting layout.
Do I cut strips across or along the fabric?
For straight binding, cut across the width, from selvedge to selvedge, which is what this calculator assumes. For bias binding, cut on the diagonal and join the strips; the fabric length figure is an estimate, so add a little extra.