Quilt backing calculator
Calculate backing yardage and cut panels from your quilt size, usable fabric width, overage and seam allowance. Compare both panel orientations or lock the fabric direction.
How much backing fabric do I need?
Measure the assembled top through its center. If you are planning new borders, enter the center before those borders and add them in the border settings. Otherwise leave planned border widths at zero. Ask your quilter how much backing must extend past each side; the editable example uses 4 inches per side.
Usable fabric width excludes selvages. A vertical-seam arrangement places full-width panels side by side; a horizontal-seam arrangement stacks panels across the quilt. Choose a direction when a print must run one way. Directional placement still does not include matching a motif or repeat.
Method and example
Required backing width and length each equal the outer top dimension plus twice the per-side overage. For n panels of usable width F and seam allowance s, the joined span is n × F − 2 × s × (n − 1). We choose enough panels to cover the target, multiply their cut length by the panel count, add your separate bolt-length reserve, then round up to the selected purchase increment.
Example: a 48 × 60 in top with 4 in overage on every side needs a 56 × 68 in backing. At 42 in usable fabric width and ½ in seams, horizontal seams need two panels cut 56 in long: 112 in of fabric, or 3.111… yd. Rounded to the next ⅛ yd, buy 3.125 yd. Vertical seams need two 68 in panels: 136 in, rounded to 3.875 yd.
Limits and cutting checks
The comparison covers two full-width panel arrangements, not every possible pieced layout. Sew the panels and trim the assembled backing to the target. Seam allowance is consumed at every joined edge. Pattern repeats, shrinkage and batting purchases are excluded; add a deliberate reserve if needed. Confirm the usable fabric width and longarm loading requirements before ordering.
Technique reference: Moda’s quilting counter guide (PDF). Calculations here use the displayed seam geometry and your own allowances.