Definition
A stitching line, or seam line, is the line along which a seam is sewn, set inside the cutting line by the width of the seam allowance.
The stitching line is where the garment's real shape is. Every measurement in a pattern, and every fit adjustment, is drafted on it; the seam allowance is only a margin added outside.
How you find it:
- Allowance included, line not printed. Many modern patterns give only the cutting line. You sew at the stated distance from the edge, using the guide lines engraved on your machine's needle plate.
- Allowance included, line printed. Some patterns print the stitching line as a dashed line inside the cutting line, which helps at corners and when fitting.
- Allowance not included. Many magazine and traditional tailoring patterns print only the stitching line. You trace it onto the fabric with chalk or a tracing wheel and add the allowance when cutting.
Stitching lines must match, not cut edges. Where two pieces meet at an angle, such as a sleeve underarm or a pointed collar, the cut edges do not line up, but the stitching lines must cross at the same point. Marking those points with a dot helps.
When fitting a toile, pin and mark changes on the stitching line, then redraw the cutting line parallel to it. Staystitching is sewn a few millimeters inside the stitching line, within the seam allowance, so it never shows.