Pattern grading is the process of turning base size or sample size patterns into additional sizes using a size specification sheet or grading increments. This can be done manually or digitally using computerized pattern drafting software.
Standard grading rules are based upon ergonomic measurements of the body, mathematically extrapolated or interpolated according to one of numerous pattern making systems. This is often chosen with an eye to the target market for a manufactured garment, in which one system or another prevails, according to consumer taste. Typically, the first pattern is developed in one size and is then graded up or down according to the chosen system, ensuring an optimum fit in all sizes.
Grading is a necessary step that must be taken before outsourcing sewing because sewists will require sets of specific patterns for cutting and sewing. (These are typically copied on to a durable medium such as oak tag paper or vinyl, and are referred to as "card sets" in the trade.) Grading will not create shape, but will only increase or decrease the size of the original shape.
Methods of Grading
There are three basic methods of pattern grading. There is not a superior method; they are all equally capable of producing a correct garment grade. These include:
Cut and spread: This is the easiest method, which acts as the basis of the other two methods. To perform this method, you must cut the pattern and spread the pieces by a certain amount to grade up, or overlap the pieces to grade down. The only tools you will need for this method are a pencil, tape, ruler, and scissors.
Pattern shifting: Pattern shifting involves increasing the overall dimensions of a pattern by moving it around at a constant distance. After you move it, you redraw the outline in order to produce the same results as cut-and-spread.
Computer grading: Computer grading is the most recent development in grading technology. It is also the fastest method. It takes the processes of the two former methods and digitizes them.