The industry standard for SA is different due to the machinery used and doesn’t follow the same guidelines as home sewing methods.
A ⅝” seam allowance is often considered the commercial pattern standard. It offers room from the edge to the stitching line to ensure each layer is joined together. For fabric that unravels easily, this seam allowance amount keeps stitches from fraying off the edge.
Areas with curves, outside edges, welt pockets, faced areas, and sleeveless armholes often have a ¼" seam allowance. It’s easiest to use this measurement when sewing around small, curved spaces.
General seams, which make up most of the seams that haven't been listed above fall into SA measurements of ⅜”, ½”. And ⅝”. When drafting patterns, SA is often left to the designer's discretion, so choose the one that’s most practical for your garment.
Bound shirt sleeves and plackets use a ⅛” SA because these areas are very narrow, and a SA allowance larger than this would create bulk in the area and would require trimming.
SA for hems also varies based on the garment and technique used and typically ranges from ¼" -3". Hems typically have at least two folds, and each fold will vary in range. Allow 1" for the hem allowance plus standard seam allowance of ⅝”.