Start with quilt top size
The default backing path begins with measured quilt-top dimensions. Finished quilt size and mattress size are different inputs. Example quilt dimensions are not the dimensions for every quilt.
Measure the assembled top
Record the assembled top’s width and length before choosing an allowance. If entering a finished-quilt planning target instead, select that measurement basis explicitly; the site does not reconstruct the original top or infer quilting shrinkage.
Add backing overhang
Enter backing overhang per side. Planning examples use different total additions, including 10 in for longarm quilting and 8 in in another backing example.
Confirm your quilter’s allowance
Your quilter may require a different amount. Use the requirement for your project and keep piecing seam allowance separate.
Use usable fabric width
Remove selvages before cutting and piecing. Enter the remaining cuttable width as usable fabric width. Do not treat a nominal width label as a verified usable measurement; measure the fabric you will cut.
Measure the cuttable span
Measure its cuttable span after identifying unusable edges; do not subtract a fixed selvage amount from the label by assumption. Keep the material’s measurement conditions consistent with the cut plan.
Read quantities separately
Distinguish base theoretical quantity, any explicitly selected reserve, quantity including reserve and recommended purchase quantity. The reserve and buying increment are separate choices; neither predicts the fabric’s dimensional shrinkage.
Choose the purchase increment
Some worked plans round calculated yardage upward to 1/4 yd. That example does not establish an increment for every shop or a layout for every quilt.
Worked backing example
Use a 60 × 80 in quilt top, 4 in overhang on each side, 40 in usable fabric width and 1/2 in seam allowance at each joined edge. Keep vertical panels and choose a 1/4 yd purchase increment for this example. These are adjustable example conditions, not universal requirements.
Theoretical quantity
The backing target is (60 + 8) × (80 + 8) = 68 × 88 in. One 40 in panel cannot cover 68 in. Two panels assemble to 2 × 40 − 2 × 0.5 × (2 − 1) = 79 in, so cut two lengths of 88 in. Total fabric length is 176 in; 176 ÷ 36 = 44/9 yd, approximately 4.89 yd.
Purchase rounding
With no reserve selected, round the unrounded 44/9 yd upward to the chosen 1/4 yd increment: ceil((44/9) ÷ 0.25) × 0.25 = 5 yd. Theoretical quantity remains 4.89 yd as displayed; recommended purchase quantity is 5 yd. A different buying increment or selected reserve can change the purchase amount.