Calculate the backing rectangle first, then the panels needed to cover it. Dividing the quilt’s area by fabric area can miss the cuts and seams that determine the yardage.
Start with the backing rectangle
Adding 4 inches at every edge turns a 60 × 80-inch top into a 68 × 88-inch backing target.
Backing width = top width + 2 × edge allowance. Length uses the same rule. A 60 × 80 top with 4 inches per edge needs 68 × 88 inches.
Confirm the allowance with your quilter. “8 inches larger overall” means 4 per edge.
Count panels after allowing for seams
42 + 42 − ½ − ½ = 83 inches assembled. The red seam band is enlarged for clarity.
N panels of usable width F, with joining allowance S, span N × F − 2S × (N − 1).
For target span A, use N = max(1, ceil((A − 2S) ÷ (F − 2S))). Two 42-inch panels with ½-inch seams span 83 inches, enough for the 68-inch target. Cut each 88 inches long.
Compare both directions
For the worked example: vertical needs 176 inches (buy 5 yards); horizontal needs 204 inches (buy 5¾ yards).
Vertical uses less length here. Different dimensions or print direction may change the choice. The calculator compares both.
Convert inches to a shopping amount
Multiply panel count by cut length and divide by 36 for yards. The purchase display rounds up to a quarter yard. Match the shop’s increments and add preparation/matching separately.
Why does a quilt-area calculation give a smaller amount?
Area alone assumes fabric can be rearranged without restrictions. Full-width cuts, seam loss, and offcuts constrain the layout, so the area minimum may not produce a usable backing.
Should I remove the selvages before entering fabric width?
Use the width that will remain available for the panels after selvages are excluded. Do not enter a label width that includes material you will cut away.
Can I make a diagonal-pieced backing with this result?
This calculator does not model diagonal piecing. Use a pattern and calculation designed for that construction method.
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