Quilt Backing Calculator

Tell it your quilt size and it works out exactly how much backing fabric to buy — and which way to run the seam.

Quilt top width (in) Quilt top height (in) Overhang per side (in) Backing fabric width (in)

Common fabric widths: 42–44" quilting cotton, 108" wide backing. Overhang gives the longarm something to grip (4" each side is typical).

You need to buy

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Vertical seams

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Horizontal seams

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Why quilt backing takes more fabric than you think

Your backing has to be bigger than the quilt top on every side so a longarm or home machine has room to baste, quilt, and square up. This calculator adds an overhang (4" per side is standard) to your finished top, then figures out how many widths of fabric you have to sew together — and how much total yardage to buy.

Vertical vs horizontal seams

Standard quilting cotton is only about 42–44" wide, so any quilt wider than that needs two or more widths seamed together. You can run those seams up-and-down (vertical) or side-to-side (horizontal). One direction almost always wastes less fabric than the other, so the tool computes both and recommends the cheaper option. Wide backing fabric (108") often covers a whole quilt with a single width and no seam at all — just change the fabric width to compare.

How to use it

Enter your finished quilt top width and height in inches.
Set the overhang per side — leave it at 4" unless your longarmer asks for more.
Enter your backing fabric width (42" for most cotton, 108" for wide backing).
Read the big number for total yardage, then check the vertical and horizontal cards to see which seam direction the tool picked and why.

FAQ

How much overhang should I leave?: Home quilters usually use 3–4" per side; longarm services often ask for 4–5". More overhang means more fabric, so ask your quilter before buying.
Why round up to eighths of a yard?: Shops cut in fractions, and you always want a little extra to square up and to allow for shrinkage after prewashing. The result is rounded up so you never come up short.
Does this include the seam allowance?: The overhang absorbs the small amount lost to seams. For very large quilts with several panels, buy a touch extra to be safe.
Is my quilt data sent anywhere?: No. Every calculation runs in your browser — nothing is uploaded or stored.

Results are estimates for planning your fabric purchase; always double-check against your quilter's requirements before cutting.