How it works
Batting width = quilt width + 2 × extra
Batting length = quilt length + 2 × extra
By the yard: one side fits the roll width; buy the other side ÷ 36, rounded up to ⅛ yd
Batting is cut bigger than the quilt top so the layers can shift a little while you quilt and still cover the edges. Longarm quilters usually ask for 4" extra on every side, because the frame needs something to hold. On a home machine or by hand, 2" per side is usually enough. The batting size is the quilt width plus twice the extra, by the quilt length plus twice the extra.
Next, the calculator checks each standard package and keeps the ones that cover the batting, either way round. It recommends the smallest of those by area, so you waste the least. Package sizes are not standard across brands: a Warm & Natural full is 90" x 96", while a Hobbs Heirloom full is 81" x 96". Check the label before you buy.
Batting by the yard comes off a wide roll. The roll width has to cover one side of the batting, and you buy the other side as length, rounded up to 1/8 yard. If the roll is narrower than both sides, you can butt two pieces edge to edge and join them with a wide zigzag. Batting has no seam allowance, so each piece only needs to cover half the span.
Worked example
A 60" x 80" quilt going to a longarm quilter needs batting 68" x 88". Crib and throw packages are too small. The twin package (72" x 90") fits with a little to spare. From a 90" roll, the 68" side runs along the roll, so you buy 68" of length, which is 2 yd.
Common mistakes
- Buying batting the same size as the quilt top. The layers shift as you quilt, and a longarm frame needs extra to clamp.
- Assuming every "queen" or "full" package is the same size. They differ by brand, so compare the inches on the label with your batting size.
- Overlapping two pieces of batting to join them. Butt the edges and zigzag them together; an overlap makes a stiff ridge that shows through.
- Forgetting shrinkage. Cotton batting can shrink 3 to 5% in the first wash; that is a look some quilters want, but plan for it if size matters.
Last checked October 2026 against standard quilting and knitting math. Found a mistake? Tell us and we’ll fix it.