# How much quilt backing do I need?

Works out how much backing fabric a quilt needs: the backing size with an overhang on each side, how many panels to sew together, and the yards to buy for regular or wide backing.

- Page: https://www.acalculator.org/everyday-life/quilt-backing-calculator
- JSON spec: https://www.acalculator.org/everyday-life/quilt-backing-calculator.json
- Version: 110a3836222c

## Default answer

Example with the default inputs (Quilt top width 60 in, Quilt top length 80 in, Extra on each side 4 in, Fabric width 42 in, Seam allowance 0.5 in): A 60 in × 80 in quilt top needs a 68 in × 88 in backing: 2 panels, seams running the length of the quilt. Buy 5 yd (4.5 m).

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| w | Quilt top width | The finished width of the quilt top. |
| l | Quilt top length | The finished length of the quilt top. |
| o | Extra on each side | How far the backing reaches past the top on every side; 4 in is common, a longarm quilter may ask for more. |
| fw | Fabric width | The usable width of the backing fabric: about 42 in for quilting cotton, 108 in for wide backing. |
| sa | Seam allowance | The seam allowance on each side of a seam that joins two panels; 1/2 in is common. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| buy | Backing to buy | The fabric length rounded up to the next 1/8 yard, and to the next 0.1 meter. |
| need | Fabric length | Panels × the length of each panel, before rounding. |
| layout | Layout | How many panels to sew together and which way the seams run. |
| panels | Panels | Widths of fabric sewn side by side. |
| backWidth | Backing width | Quilt width + 2 × the extra on each side. |
| backLength | Backing length | Quilt length + 2 × the extra on each side. |
| yards | Yards to buy | Rounded up to the next 1/8 yard. |

## Method

Backing = (width + 2 × extra) by (length + 2 × extra); panels = ⌈(span − 2 × seam) ÷ (fabric width − 2 × seam)⌉ each way; buy the smaller of panels × the other side, rounded up to 1/8 yd.

## Assumptions

- Panels are sewn side by side with one seam between neighbours; each seam uses the seam allowance on both panels.
- The fabric has no one-way print, so a panel can run either way.
- The length is rounded up to the next 1/8 yard (or 0.1 m), as fabric is usually cut.

## Worked examples

1. w = 1.524, l = 2.032, o = 0.1016, fw = 1.0668, sa = 0.0127 gives panels = 2, need = 4.4704, yards = 5, buy = 5 yd (4.5 m), backWidth = 1.7272. Source: NIST Handbook 44 (2026), Appendix C, General Tables of Units of Measurement (1 yard = 36 inches; 1 inch = 2.54 centimeters exactly), https://www.nist.gov/document/2026-nist-handbook-44-appendix-c (retrieved 2026-10-03).
2. w = 1.524, l = 2.032, o = 0.1016, fw = 2.7432, sa = 0.0127 gives panels = 1, need = 1.7272, yards = 2, buy = 2 yd (1.8 m), layout = One piece, no seams. Source: NIST Handbook 44 (2026), Appendix C, General Tables of Units of Measurement (1 yard = 36 inches; 1 inch = 2.54 centimeters exactly), https://www.nist.gov/document/2026-nist-handbook-44-appendix-c (retrieved 2026-10-03).
3. w = 2.286, l = 2.7432, o = 0.1016, fw = 1.0668, sa = 0.0127 gives panels = 3, need = 7.4676, yards = 8.25, layout = 3 panels, seams running across the quilt. Source: NIST Handbook 44 (2026), Appendix C, General Tables of Units of Measurement (1 yard = 36 inches; 1 inch = 2.54 centimeters exactly), https://www.nist.gov/document/2026-nist-handbook-44-appendix-c (retrieved 2026-10-03).

## FAQ

### How much bigger should quilt backing be than the top?

About 4 in on every side, so 8 in wider and 8 in longer than the top, is a common choice for quilting at home. A longarm quilter often asks for 4 in to 8 in on each side, because the frame clamps the backing; ask yours before you buy.

### How much backing do I need for a 60 × 80 in quilt?

With 4 in extra on each side the backing is 68 × 88 in. On 42 in wide cotton that is 2 panels of 88 in, 176 in, which rounds up to 5 yards. On 108 in wide backing, one 68 in cut turned sideways is enough: 2 yards.

### Should the seams run the length of the quilt or across it?

Either works. Seams that run the length are more common, but on a wide quilt, seams across can need fewer panels or shorter ones. The calculator works out both ways and shows the one that needs less fabric.

### What is the usable width of quilting cotton?

Quilting cotton is sold as 44 in or 45 in wide, but after the selvages are cut off and the fabric is washed, about 40 in to 42 in is usable. Use 42 in, or measure your own fabric.

### What is wide backing?

Fabric made for quilt backs, usually 108 in wide (sometimes 90 in or 120 in). It covers most quilts with no seams.

### Why add the seam allowance?

Each seam that joins two panels uses the seam allowance on both of them, so two 42 in panels joined with a 1/2 in seam make 83 in, not 84 in.

## Sources

- NIST Handbook 44 (2026), Appendix C, General Tables of Units of Measurement (1 yard = 36 inches; 1 inch = 2.54 centimeters exactly). https://www.nist.gov/document/2026-nist-handbook-44-appendix-c (retrieved 2026-10-03)
- Deb’s Quilt Studio, Choosing the Right Quilt Backing Fabric (a longarm quilter asks for backing several inches larger than the top on each side, and prefers 108 in wide backing). https://debsquiltstudio.blog/choosing-the-right-quilt-backing-fabric/ (retrieved 2026-10-03)