How to calculate quilt backing

Add 4″ to every side of the quilt top, work out how many 40″ panels cover that width, and multiply by the length. A 90″ × 108″ queen quilt needs 8 1/4 yd of regular cotton. Drag the sliders below and watch it happen.

Backing simulator

Units Inches & yards Centimetres & metres

Quilt width

Quilt length

Extra on every side

Backing fabric Regular cotton, 42–44″Wide backing, 108″ Seams Whichever uses leastRun downRun across

Try: Baby 36 × 52Throw 60 × 70Twin 70 × 90Queen 90 × 108King 108 × 108

▶ Play the steps ‹ Back Next ›

1. Measure the topThe finished quilt top, edge to edge, after trimming.
2. Add the extra4″ on every side so the quilter can clamp and square the edges.
3. Cut the panelsEach panel is a full width of fabric, about 40″ usable.
4. Sew the seamsJoin panels with ½″ seams. One seam direction usually costs less.
5. Buy the lengthAll the panels, end to end, rounded up to the next ⅛ yard.

Step by step

1. Measure the quilt top across and down, through the middle, not along the edges (edges stretch). Call these W and L.
2. Add the extra. Backing width = W + 8″ and backing length = L + 8″ (4″ per side). A queen 90″ × 108″ top becomes 98″ × 116″.
3. Count the panels. Cotton gives about 40″ per panel after trimming selvages and a ½″ seam. If the backing is 98″ wide you need three panels, because two give only 79″.
4. Multiply by the panel length. Seams running down: 3 panels × 116″ = 348″ = 9 3/4 yd.
5. Try the other way. Seams running across: 3 panels × 98″ = 294″ = 8 1/4 yd. Buy the smaller.
6. Round up to the next ⅛ yard (about 10 cm) so a slightly crooked cut does not leave you short.

Worked examples

Want a number for your own size without the animation? Use the quilt backing calculator, or see the full method and assumptions.

Questions quilters ask

How do you calculate the backing fabric for a quilt?

Add 4 inches to each side of the quilt top (8 inches to the width and the length). Divide that backing width by about 40 inches, the usable width of 42-44 inch cotton, and round up to get the number of panels. Multiply the panels by the backing length. A 90 x 108 inch queen quilt needs 3 panels and 8 1/4 yd.

How much bigger should the backing be than the quilt top?

Four inches on every side is the usual amount for long-arm quilting, because the machine clamps the edges. Some long-arm quilters ask for 5 or 6 inches. For quilting on a home machine 2 to 3 inches per side is enough.

Why use 40 inches and not the 42 or 44 inches on the bolt?

Quilting cotton is 42 to 44 inches wide, but the selvages and the first inch or so are trimmed off, and each seam costs another half inch. About 40 inches per panel is a safe number that does not leave you short.

Should the backing seams run down or across the quilt?

Work out both and buy the smaller amount. For a 90 x 108 inch quilt, seams that run across need 8 1/4 yd and seams that run down need 9 3/4 yd. If your long-arm quilter has a preference for how the quilt loads on the frame, ask first.

When is wide backing worth it?

Wide backing is 108 inches wide (about 104 usable), so a quilt up to about 96 inches wide needs no seam at all. A 90 x 108 inch quilt takes 3 1/4 yd of it, in one piece.

Keep learning

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• Free calculator Quilt backing calculator Just want the number? Type your size and get it straight away.

Updated 2026-11-14.