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Calculate how many yards of fabric you need for a sewing project. Plan pattern layout, width, and repeats to buy the right amount of material.
Calculate quilt backing fabric needed including overhang and seam allowance. Size backing for longarm, domestic machine, or hand quilting projects.
Calculate continuous bias tape length from a square of fabric. Find strip width, yardage, and join count for quilt binding and garment finishing.
Commercial patterns often use ⅝" (1.5 cm) at seams and ¼" on hems. Custom adjustments shift cut edges outward or inward from stitch lines.
New cut line = stitch line ± seam allowance changeVertical adjustments at lengthen/shorten lines preserve seam allowance at unchanged seams — only internal length changes.
Finished length change = cut line movement at adjustment lineFrench seams consume more fabric inside — add extra allowance when converting from single to enclosed seams.
French seam total allowance ≈ ⅜" to ½" finished from edgeUpdated: July 2026
Each side seam releases ½ inch per side from existing allowance — verify at least ⅝" remained before alteration.
Trim ½ inch from shoulder cut line at armscye while keeping ⅝" allowance at new seam — net shoulder width reduces ½ inch.
Convert ½ inch total to flat-felled: trim one side, fold — calculator shows starting allowance must be ≥⅝ inch per leg seam.
Move cut edge by the same amount as stitch line change plus maintain constant seam allowance width.
Insufficient allowance causes fraying and weak seams on curves. Match or exceed pattern-specified allowance when re-cutting.
Seam allowance is the fabric between stitch line and cut edge — typically ⅝ inch in commercial patterns. When altering seams, merging pieces, or converting to flat-felled seams, calculate new cut lines so finished dimensions stay correct.