How Do You Calculate Quilt Backing and Binding?

Worked Example: A 180 x 220cm Quilt Top

Backing (default settings: 10cm overhang each side, 112cm fabric, 2cm selvedge trim, 1.5cm seam allowance):

• Backing width = 180cm + (10cm × 2) = 200cm
• Backing length = 220cm + (10cm × 2) = 240cm
• Usable fabric width = 112cm − 2cm selvedge = 110cm
• 200cm is wider than the 110cm usable fabric, so panels need joining. One panel only reaches 110cm, not enough. Two panels give a raw width of 2 × 110cm = 220cm, but the seam joining them consumes 1.5cm from each side it touches (3cm total), so the assembled width is 220cm − 3cm = 217cm, which covers the 200cm needed
• Fabric needed = 2 panels × 240cm = 480cm = 4.8m

Binding (default settings: 25cm extra allowance, 6.5cm double-fold strips, 2cm selvedge waste):

• Perimeter = 2 × (180cm + 220cm) = 800cm
• Binding length = 800cm + 25cm = 825cm
• Usable fabric width = 112cm − 2cm selvedge = 110cm
• Strips needed = 825cm ÷ 110cm = 7.5, rounded up to 8 strips
• Fabric needed = 8 strips × 6.5cm = 52cm = 0.52m, rounded up to the nearest 0.1m = 0.6m

Backing and binding are usually cut from different fabrics, so this quilt needs roughly 4.8m of backing fabric plus 0.6m of binding fabric, not one combined total. The quilt backing calculator and quilt binding calculator run both of these for your own quilt dimensions.

Why Backing Needs More Fabric Than You Might Expect

The jump from “2 panels should be plenty” to needing the fabric that calculation implies catches people out: joining panels does not just add width, it also removes some. Every seam eats 1.5cm of fabric from each side it joins, so two panels of 110cm usable width do not give you 220cm of finished width, they give you 217cm. For quilts close to double the usable fabric width, that seam loss can be the difference between two panels being enough and needing a third. Most quilting cotton is 112cm wide, so for quilts wider than about 110cm you need to seam two or more panels of backing together; wide backing fabric (274cm) is available and avoids seaming altogether, but costs more per metre.

Binding Strip Width: Double-Fold vs Single-Fold

For double-fold binding, the most common finish, cut strips 6–6.5cm wide: 6.35cm is the 2.5-inch quilting standard, folded in half and machine-sewn to finish at roughly 6mm–1.25cm on the front depending on your seam allowance. For single-fold binding, 4cm strips give about 1cm of finished binding. Strips are cut across the width of the fabric and joined with diagonal (45-degree) seams for a smooth transition: place two strips right sides together at right angles, sew along the diagonal, trim to 0.6cm and press open.

Getting the Overhang Right

Backing (and batting, if you use it) should extend 8–10cm beyond the quilt top on every side. That margin gives a long-arm quilter or quilting frame something to grip while it works, and the excess is trimmed away once quilting is finished. Binding does not need an overhang in the same way: it is cut to the quilt's actual perimeter plus a fixed 25cm allowance for joining strips, turning corners and overlapping the start and finish.