Quilt Backing Calculator

Estimate the backing rectangle, panel count and linear fabric needed for a pieced quilt back. Compare vertical and horizontal seam layouts when the fabric is non-directional.

Scope: panels are cut as full usable fabric widths and joined with the seam allowance entered above. “Use least fabric” may rotate the panel layout by 90°, so use vertical seams only for directional prints or when fabric orientation matters.

How it works

Backing width and length equal the quilt-top dimensions plus the selected extra margin on both sides. For each possible seam direction, the calculator finds the smallest whole number of fabric-width panels whose joined coverage is large enough.

Joining seam loss

Every join uses seam allowance from both adjacent panels. Joined coverage therefore equals panel count × usable fabric width minus twice the seam allowance for each join.

Before buying

Long-arm quilters can have their own preferred backing margin. Pattern matching, centred motifs, pieced decorative backs and prewashing may require additional fabric beyond this geometric estimate.

Worked example

A 150 × 200 cm quilt with 10 cm extra backing on every side needs a 170 × 220 cm backing. With 106 cm usable fabric width and 1.25 cm joining seam allowance, two vertical panels cover the width and require 4.40 m of linear fabric.

Common question

Why might the horizontal layout use less fabric? For non-directional fabric, rotating the panel layout can reduce the number or length of full-width cuts. The calculator compares both options when requested.

Related quilting tools

Quilt Binding Calculator · Quilt Block Calculator · Fabric Yardage Calculator