How to Prepare Quilt Backing for Longarm Quilting
Get the quilter’s backing requirements before you buy fabric. A mathematically sufficient back can still be awkward to load if it lacks the margin their machine needs.
Confirm the extra fabric on every edge
The calculator starts with 4 inches per side; longarm quilters often ask for 4–6. Their instructions take priority. Ask whether the requested amount is per side or added to the whole dimension, and whether any mounting method needs a different allowance.
For a 70 × 90-inch top, 4 inches per side gives a 78 × 98-inch backing rectangle. A request for 6 inches per side changes that to 82 × 102 inches. This can change the number of panels, not just the cut length.
For example, two panels at 40 usable inches with ½-inch seam allowances cover 79 inches. They cover the 78-inch width, but not 82 inches. Recalculate after changing overhang instead of simply adding a little to the old purchase amount.
Discuss seam direction and the print
Send or describe the proposed cut plan before sewing if you are unsure how the machine will load it. Confirm which edge of a directional print is the top. Also flag any large motif you want positioned deliberately; the calculator centers a simple rectangle and cannot plan that placement.
Follow the quilter’s seam requirements. The calculator’s default is a ½-inch allowance on each joined edge. Trim selvages out of joins and press as requested; APQS discusses open seams and backing construction in its pieced-back guidance.
Prepare the actual piece
- Check fabric care first. If you will prewash, wash before final measuring and cutting. Use the prewash guide to separate width changes from extra purchase length.
- Measure usable width. Exclude selvages and allow for any damage or uneven edges you cannot use.
- Cut and join the planned panels. Check the number, direction, and cut length against the printed list before making the first cut.
- Check the assembled rectangle. Measure again after sewing and pressing. Confirm that it meets the requested width and length throughout.
- Confirm the handoff. Ask how the quilter wants the top, backing, and batting delivered, and how they want the top edge identified.
Use the diagram as a size check
The dashed quilt top in the cut diagram helps you see the planned surrounding margin. It is not a prescription for positioning the top on a longarm frame. Loading can place the quilt differently within that spare fabric; follow your quilter’s process.
Keep the backing overhang separate from batting requirements. This tool calculates backing fabric only. Also reserve extra length if you need to square a crooked shop cut or match a print: neither is included automatically.