How to use the quilt backing calculator
- Choose a standard quilt size or enter your finished quilt top’s width and length.
- Set the extra on each side — 4 inches for longarm quilting, 2–3 inches for quilting at home.
- Enter the usable width of your backing fabric: about 42 in for quilting cotton or 108 in for wide backing.
- Read the yardage to buy and how many panels to sew together.
How it is calculated
Backing size = (Quilt width + 2 × extra) × (Quilt length + 2 × extra) Panels = widths needed to cover one side, allowing ½ in per seam Vertical seams: Panels × Backing length Horizontal seams: Panels × Backing width Buy the smaller of the two, rounded up to ⅛ yard
Worked example
A 60 × 80 in quilt, 4 inches extra per side, on 42 in fabric:
- Backing size = 68 × 88 in
- Vertical seams: 2 panels × 88 in = 176 in
- Horizontal seams: 3 panels × 68 in = 204 in
- Use vertical seams: 176 in = 4.89 yd → buy 5 yards
Backing yardage for common sizes (4 in extra per side)
| Quilt | Size | 42 in fabric | 108 in wide back |
|---|---|---|---|
| Baby | 36 × 52 in | 2½ yd | 1¼ yd |
| Throw | 60 × 70 in | 3⅞ yd | 2 yd |
| Twin | 70 × 90 in | 5½ yd | 2¼ yd |
| Full | 85 × 108 in | 7¾ yd | 3¼ yd |
| Queen | 90 × 108 in | 8¼ yd | 3¼ yd |
| King | 108 × 108 in | 9¾ yd | 6½ yd (two widths) |
For a king, the 116 in backing is wider than 108 in fabric, so even wide backing needs a seam — or ask your longarmer whether 3–4 in per side is enough.
Tips for a smooth backing
- Remove selvages before sewing panels together — they shrink differently and can pucker.
- Press seams open to reduce bulk where the quilting crosses them.
- Square the backing and mark the centre of each side to help load it straight.
- Prewash consistently: if you prewashed the top fabrics, prewash the backing too.
- Directional prints: if the print has a direction, check which seam orientation keeps it upright.
- Use the leftovers: offcuts from the backing often make a matching binding — see the quilt binding calculator.
Choosing backing fabric
Quilting-weight cotton is the classic choice and matches the top’s shrinkage. Busy prints hide quilting stitches and small mistakes on the back, while solids show off the quilting design. Minky and flannel make cosy backs but stretch or shrink more, so baste them carefully. Wide backing saves sewing time and avoids seams entirely on most quilts up to queen size.
If you are short by a few inches, a pieced backing with a contrasting strip or leftover blocks down the middle stretches the fabric you have and adds a fun detail to the back.