Quilt backing must be larger than the top so it can be clamped on the frame and so the layers can shift slightly during quilting. Most longarm quilters ask for 4 in extra on every side. Standard 42–44 in quilting cotton usually needs to be seamed; wide backing fabric (108 in) avoids seams.
How to use the Quilt Backing Calculator
- Quilt top width
- Quilt top length
- Overage on each side
- Backing fabric width (usable)
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the width and length of the quilt top, the overage per side and the usable width of the backing fabric.
Tips
- Measure over thin clothing with a soft tape held snug but not tight, and keep the tape level all the way round.
- Take each measurement twice; if you are between sizes, the larger size is usually the safer choice.
- Size charts vary by brand and country – check the maker’s own chart when it is available.
- For sewing projects, pre-wash fabric before cutting and buy 10% extra for shrinkage, pattern matching and mistakes.
Common mistakes to avoid
- Mixing inches and centimetres between the tape and the size chart.
- Forgetting seam and hem allowances when cutting fabric.
- Measuring an old, stretched garment instead of your body.
Inputs explained
| Field | What to enter |
|---|---|
| Quilt top width | Units: in, cm |
| Quilt top length | Units: in, cm |
| Overage on each side | Units: in, cm |
| Backing fabric width (usable) | Choose one: 42 in (quilting cotton), 54 in, 60 in, 90 in (wide back) … |
What each result means
- Backing width needed = [Quilt top width] + 2×[Overage on each side]
- Backing length needed = [Quilt top length] + 2×[Overage on each side]
- Widths if seams run vertically = ceil([Backing width needed]÷[Backing fabric width (usable)] – 0.000001)
- Widths if seams run horizontally = ceil([Backing length needed]÷[Backing fabric width (usable)] – 0.000001)
- Fabric to buy = min([Widths if seams run vertically]×[Backing length needed], [Widths if seams run horizontally]×[Backing width needed])
Example values
How the main result changes when Quilt top width changes and everything else stays at the example values above:
| Quilt top width (in) | Fabric to buy (yd) |
|---|---|
| 30 | 2.44 |
| 45 | 4.42 |
| 60 | 4.89 |
| 75 | 4.89 |
| 90 | 7.33 |
| 120 | 9.78 |
Formula
Backing size = quilt top + 2 × overage (4 in each side for longarm quilting)Widths needed = ceil(backing width ÷ fabric width)Fabric length = widths × backing length; yards = inches ÷ 36Worked example
Inputs — Quilt top width: 60 in; Quilt top length: 80 in; Overage on each side: 4 in; Backing fabric width (usable): 42 in (quilting cotton).
Results — Backing width needed = 68 in; Backing length needed = 88 in; Widths if seams run vertically = 2; Widths if seams run horizontally = 3; Fabric to buy = 4.89 yd.
Frequently asked questions
How much backing for a queen quilt?
A 90 × 108 in top needs about 9 yards of 42 in fabric, or 3¼ yards of 108 in wide backing.
How much bigger should backing be?
4 in on every side for longarm quilting; 2–3 in for domestic-machine quilting.
Should backing seams be vertical or horizontal?
Either – choose the layout that uses less fabric; the calculator compares both.
What formula does the Quilt Backing Calculator use?
Backing size = quilt top + 2 × overage (4 in each side for longarm quilting).