Quilt Backing Calculator
Determines how many yards of backing fabric to buy for any quilt, accounting for overhang, piecing seams, and pre-wash shrinkage. Use it before shopping to avoid running short.
Last updated: September 2026
Backing Fabric Needed
5.25 yards
Formula below · 1 source (missouriquiltco.com) · Updated Sep 2026
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About this calculator
Quilt backing must extend beyond the quilt top on all sides — typically 2–4 inches, more for longarm quilting — so the backing is (quiltWidth + 2 × overhang) by (quiltLength + 2 × overhang). Backing has to be cut in whole fabric widths: if the backing is wider than one usable width of fabric (the bolt width minus about 2 inches for selvages and the seam), you need two or more full-length panels seamed together, or panels run crosswise. The calculator works out both layouts, panels = ⌈backing width ÷ usable width⌉ lengths of the backing length, or ⌈backing length ÷ usable width⌉ lengths of the backing width, and uses whichever needs less fabric. That is why a quilt slightly wider than one width needs about twice the yardage its area suggests. The yardage is then increased by the shrinkage allowance and rounded up to the next quarter yard, the smallest cut most shops sell: yards = ⌈4 × panels × panel length × (1 + shrinkage/100) ÷ 36⌉ ÷ 4. Cotton quilting fabric typically shrinks 2–5% when pre-washed.
Longarm quilters usually ask for 4–6 inches of extra backing on every side; 2–3 inches is often enough for quilting on a home machine. Piece backing seams with about a ½-inch seam allowance and press them open.
How to use
Enter the finished quilt top size, choose the backing fabric width, and set the extra backing per side and a shrinkage allowance (0 if you pre-wash). Example 1 (the defaults): a 60 × 80 in top, 42 in fabric, 4 in per side, 3% shrinkage. Backing 68 × 88 in; usable width 40 in, so two 88 in panels (176 in) beat three 68 in panels (204 in). 176 × 1.03 = 181.3 in = 5.04 yd, rounded up to 5¼ yards. Example 2: the same top on 44 in fabric with 3 in per side: backing 66 × 86, two 86 in panels = 172 in, × 1.03 = 4.92 yd, so buy 5 yards. Example 3: the default top on 108 in wide-back (106 in usable): the 88 in length fits across the fabric, so one 68 in cut does it: 68 × 1.03 ÷ 36 = 1.95 yd, so buy 2 yards.
Frequently asked questions
Why do I need extra backing fabric beyond the quilt top size?
The backing must extend past all four edges of the quilt top — usually 2 to 4 inches per side — so it can be secured in a quilting frame or hoop without slipping. This overhang is trimmed away after quilting is complete. Skipping the overhang allowance is one of the most common causes of backing that comes up short mid-project.
How much shrinkage allowance should I add for quilt backing fabric?
Most 100% cotton quilting fabrics shrink between 2% and 5% when washed and dried. A safe standard allowance is 3%, which this calculator uses as a default. Pre-washing your fabric before cutting is strongly recommended, but adding the shrinkage allowance ensures you buy enough yardage even if you skip that step.
When should I piece quilt backing with two fabric panels instead of one?
You need two panels when the quilt width plus both overhangs exceeds the usable width of your backing fabric. Standard quilting cotton is 44–45 inches wide, while wide-back fabric is 108 inches wide. Choosing a wide-back fabric for large quilts can eliminate the need to piece the backing at all, saving both time and a visible center seam.
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