Quilt Backing Seam Layout Calculator

How to use this estimate

The backing must cover the top plus twice the border on both dimensions. A strip count must leave enough combined width after each join consumes two seam allowances. The extra squaring allowance is applied to every full-width strip, so it is a conservative per-strip allowance. Compare total bolt length for both orientations, then verify grain, print direction, and actual usable bolt width.

Method

Backing spans are top width + 2 × border and top length + 2 × border. For each orientation, choose the smallest strip count n for which n × usable fabric width - 2 × seam allowance × (n - 1) covers the perpendicular span. Total bolt length = strips × (other backing span + per-strip squaring allowance); yardage = total bolt length / 36.

Worked example

With a 60 × 80 in quilt, 4 in border, 42 in usable width, ½ in seams, and 8 in squaring allowance per strip, the vertical layout uses 2 strips cut 96 in long, or 192 in (5.33 yd) total. The horizontal option uses 3 strips cut 76 in each, or 228 in (6.33 yd), so vertical is shorter.

Assumptions and supported inputs

Use measured dimensions and the listed field ranges. Values outside those bounds, missing entries, non-finite numbers, and fractional counts where a whole number is required are rejected. Displayed results are rounded to two decimal places; internal calculations retain full precision. This is a planning estimate, not a substitute for an on-site layout, product instructions, or a qualified trade decision where applicable.

Related planning tools

fabric shrinkage yardage calculator · wallpaper roll calculator

Northstar Calculators provides this arithmetic for scenario planning. Verify the assumptions and physical fit before buying or building.