Once the sampling is finished and the designs approved the patterns need to be graded into different sizes.
The purpose of grading is to proportionally increase or decrease the size of a pattern, while maintaining shape, fit, balance and scale of style details. The grader will need to know what sizes you want to grade against i.e. Marks & Spencers or Next and what sizes you want for example small, medium or large; UK 8, 10, 12 or 14 or 32, 34 or 36 inches.
To properly fit a pattern to a range of sizes each pattern piece needed to be graded or systematically increased or decreased. Pattern graders take a middle-sized pattern (typically a size 12) and grade it up for larger sizes and grade it down for smaller sizes.
There are three basic methods of grading: cut and spread, pattern shifting, and computer grading. No one method is technically superior and all are equally capable of producing a correct grade.
The easiest method, which is the basis of the other two methods, is to cut the pattern and spread the pieces by a specific amount to grade up, or overlap them to grade down. No special training or tools are required - just scissors, a pencil, tape, and a ruler.
Pattern shifting is the process of increasing the overall dimensions of a pattern by moving it a measured distance up and down and left and right, (using a specially designed ruler) and redrawing the outline, to produce the same results as the cut-and-spread method.
This used to be only available to big manufacturers and is by far the fastest method. However, sophisticated home computer software is becoming affordable and many freelance designers are now using this method.
It's important to remember that grading only makes a shape larger or smaller and isn't intended to change a shape. Grading also reflects the fact that individuals of different sizes are proportionately different not uniformly different. When patterns are graded up or down they don't merely make everything equally larger or smaller. Instead the grader takes into account that different body parts increase at different and proportional amounts.
Grading vs. alteration: What's the difference?
Grading is used to increase or decrease a size, based on an average difference between sizes.
Alteration is used to make a particular size conform to an individual's personal figure challenges.