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.
About this calculator
Quilt backing must extend beyond the quilt top on all sides — typically 2–4 inches — to allow for quilting hoop grip and trimming. The calculator first checks whether the quilt width plus overhang on both sides fits within a single fabric width. If it does, one length of fabric suffices; if not, two lengths must be seamed together side by side. The core formula is: yards = ⌈(quiltLength + overhang × 2) × panels × (1 + shrinkage/100) / 36⌉, where panels is 1 or 2 depending on the width check. Dividing by 36 converts inches to yards, and Math.ceil rounds up to the next whole yard so you never under-buy. The shrinkage multiplier pre-accounts for the fact that cotton fabric typically shrinks 2–5% when washed before use.
How to use
Suppose your quilt top is 60 inches wide × 80 inches long, you're using 44-inch-wide fabric, you want a 3-inch overhang, and you expect 3% shrinkage. Step 1 — check width: 60 + (3 × 2) = 66 inches, which exceeds the 44-inch fabric width, so you need 2 panels. Step 2 — calculate length needed: (80 + 6) × 2 × (1 + 3/100) = 86 × 2 × 1.03 = 177.16 inches. Step 3 — convert to yards: 177.16 / 36 = 4.92 yards. Step 4 — round up: ⌈4.92⌉ = 5 yards. You should purchase 5 yards of backing fabric.
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.