Learn How To Grade Your Seam Allowances For Dressmaking Once you have sewn a seam in dressmaking, or in most other sewing projects for that matter, your pattern instructions may ask you to grade the seam allowances.  This means to trim each layer to a different level so they are tiered. The purpose of grading seam allowances is to reduce any bulkiness in that area and to help prevent the seam raw edges from leaving an imprint or ridge on the right side of the garment or sewin