How Much Backing Fabric Do I Need?
Measure the quilt top first. Backing yardage depends on the extra fabric around it, the usable width of your fabric, and which way you join the panels.
Start with the backing rectangle
Measure the completed top, including borders, laid flat without pulling it. Add your overhang twice to each dimension: once for each opposite edge. For a 60 × 72-inch top with 4 inches on every side, the backing must cover 68 × 80 inches.
The overhang setting is per side, not the total extra width. If your longarm quilter asks for 6 inches, that same top needs 72 × 84 inches. Use their requirements before choosing a fabric quantity.
Allow for the joins
A bolt’s labeled width is not necessarily its usable width. Measure between the selvages, and use the width after washing if you will prewash. This calculator starts standard cotton at 40 usable inches; replace that with your own measurement.
Two 40-inch panels joined with a ½-inch allowance on each edge cover 79 inches: 40 + 40 − 1. Three cover 118 inches: 120 − 2. Every join uses two seam allowances. One panel needs no join allowance.
A worked example: a 60 × 72-inch throw
Use 4-inch overhang, 40-inch usable width, ½-inch seam allowances, and no prewash allowance. Compare these two layouts:
- Vertical seam: two panels, each cut 80 inches long. The total purchase length is 160 inches. Divide by 36 and round up to the next eighth: 4½ yards, or independently 4.1 meters.
- Horizontal seams: three panels, each cut 68 inches long. The total is 204 inches, which rounds up to 5¾ yards, or 5.2 meters.
The vertical plan saves 44 inches before rounding. After joining, its backing measures 79 × 80 inches. Trimming its width to 68 inches leaves an 11 × 80-inch strip, before any extra squaring or quilting losses.
Turn the estimate into a purchase
Yards round up to ⅛ yard; meters round up separately to 0.1 meter. The two displays are purchase quantities, so converting one rounded result may not exactly equal the other. If a shop sells only quarter yards, round the yard result up again to its next quarter.
Add any fabric you need for matching a print or squaring uneven ends. The tool estimates straight, full-width panels; it does not optimize diagonal piecing or an assortment of scraps. Save the cut list and check it against the fabric before cutting.
Next: choose a seam direction, or see when wide backing saves a seam.