Quilt Backing Calculator
Enter the size of your finished quilt top. We'll calculate how much backing fabric to buy and how to piece it.
How we calculate it
- Add extra fabric on every side of the quilt top. 4 in per side is standard and works for a longarm, so a 60 × 72 in top needs a 68 × 80 in backing.
- If you'll prewash, add 5% to the width and the length. Cotton can shrink more one way or the other, so we allow for both.
- Count how many pieces you need. Quilting cotton is 44–45 in wide, with about 42 in usable once the selvages are trimmed. Each 1/2 in seam uses 1 in.
- Multiply the number of pieces by the length of each piece. Divide by 36 to get yards.
- Round up to the next 1/4 yd, which is how we cut.
Why horizontal seams?
We piece backings with horizontal seams, running across the quilt. On a longarm frame, they lie parallel to the rollers, so the backing rolls on evenly with steady tension.
On some large quilts, vertical seams use less fabric. When they save 1/2 yd or more, the calculator shows that option too.
Why the extra inches?
The quilt sandwich shifts and draws up as you quilt. Extra backing keeps the edges covered.
4 in per side is plenty for most longarm quilters, who clamp the backing to their frame. Choose 6 in if you'd like extra room.
Seams on a pieced back
Trim off the selvages first. Sew with a 1/2 in seam and press it open, so it lies flat and holds up under the tension of a quilting frame.
Backing with 60 in fabric
60 in fabric has about 58 in usable once the selvages are trimmed. Crib quilts need just one piece and no seams, and most throws need only one seam.
Backing for common quilt sizes
With 4 in extra per side and horizontal seams, without prewashing.