Calculators

Piece a backing with one diagonal seam

The Diagonal backing calculator uses John Flynn's method to widen one length of fabric with a diagonal seam, and says whether that beats seaming straight panels.

Where to find it

Studio top bar → Calculators → Diagonal backing. Also at quiltler.com → Calculators, and in the Calculators tab of the iPhone and iPad app.

Open the diagonal backing calculator
On the Diagonal backing calculator, changing the quilt width from 48 to 52 inches gives 2 7/8 yards: cut 101 inches of 44 inch fabric and widen it to 58 inches with one diagonal seam, against 3 1/4 yards seamed straight

How to do it

  1. Press Calculators in the studio's top bar and choose Diagonal backing. It opens on a 48 × 60″ quilt on 44″ fabric, with the answer already in the You need card.
  2. Type your Quilt width (inches) and Quilt length (inches), and the Overhang each side (inches) you want.
  3. Set Usable fabric width (inches) to your backing fabric's width.
  4. Read the card: the backing size, the Diagonal yardage, the Fabric to cut before the seam, and the Straight-grain yardage to compare.
  5. If straight seams use the same or less, the card says so. Then use the ordinary Backing calculator.

Good to know

  • It pays when the backing is wider than the fabric but no more than about one and a half widths.
  • The seam is on the bias and stretches: pin it, use a walking foot and press it open.
Who can use it
Free, no account needed on the web
Where it works
Web studio · quiltler.com · iPhone & iPad

This guide answers

  • How do I make a backing a little wider than my fabric?
  • What is the John Flynn diagonal backing method?
  • Does a diagonal seam save backing fabric?
  • My backing is a bit too narrow for my quilt
  • How long a piece do I cut for a diagonally pieced back?