All American commercial sewing patterns have a set seam allowance of 5/8" (or 15mm) which is where the sewer needs to stitch the fabric.
Seam allowance is the space between the sewing machine needle and the edge of the fabric.
This is important because a sewing pattern has included this space within its pattern and to have a true to size fit, the sewer needs to sew this way. Most sewing machines have an indication on the sewing plate with some lines and the sewer can use this as their "guide" when sewing a garment.
