What are grade specs, grade rules and grade rule libraries?

In the process of writing a post, I find I need this post in order to be able to refer to it.

There are three levels or layers of size specification:

  1. Grade specifications (varies from general to specific)
  2. Grade rules
  3. Grade rule libraries

I will do grade specifications last.

girth_rules_mapped2A grade rule is a designated amount a pattern is made larger or smaller at one given point in order to make it fit a range of sizes.

[The “one given point” at which a grade rule is placed is called a cardinal point. The grading police will not come and get you if you don’t know this.]

In the illustration at right, there are grade rules placed at the (cardinal points) neck and shoulder juncture, the outside shoulder tip and midway down through the armhole. The illustration is only a visual example that shows how a manual pattern is mapped. A CAD pattern is graded at the same cardinal points of course but it doesn’t look like this on screen. A discussion of grade mapping is in my book in the section titled A practical guide to grading starting on pages 170-175. Because designers are not expected to specify grade rules, there will not be a test on this later.

A grade rule library is a collection of grade rules that will be used to grade a pattern according to the desired size specifications. I realize that the word “Library” conjures up the idea of a large collection but a library amounts to a chart of data. It’s a library in that it is a “collection” but not in that it is large.

Each library will vary according to the type of grade, features and fabric properties of a design. For example, you will need two different libraries for two identical tops if one is knit and the other is a woven. Or, you will need two different libraries if one of the tops is graded SML and the other in numbered sizes. Grade rule libraries are usually made by copying and pasting data from one or more rule libraries to create new ones. Again you don’t have to worry about this. I cannot think of an instance in which a designer would be responsible for creating grade rule libraries unless they wanted to.

Grade specifications are relatively general but can be more complex depending. A grade spec is a measure you specify to indicate how much you want each size to grow or shrink (this is also in my book in the grading section I mentioned). You should know something about sizing to know whether you want each size to increase an inch or two and also for height. There are several earlier entries about this on this site that I will link to at close.

More complex grade specs are appropriate if you are targeting a specific niche but again, you need to know something about grading and in that case, probably won’t be reading this except to double check yourself because it seems like half the time that the rest of the world has gone crazy so you begin to wonder if it’s you or everyone else.

The bad news is that designers are expected to provide basic (simple) grade specifications. This is your job. If you don’t know or have them, you can usually hire a pattern maker or grader to help you develop them. However, it is very important that you know this is not our job. Many designers are annoyed if service providers can’t guess what one’s grade specs should be or angry that we don’t provide this service for free. Collecting information like this can be expensive but you can do it yourself for a relatively low cost. Worst case, you can buy a range of sizes of an existing product line of which you like the grade, take these to a pattern grader who can then measure each garment to reverse engineer the grade.

Related:
How to create grade rules pt.1
How to create grade rules pt.2
How to create grade rules pt.3
Things you must know if you have a clothing line: garment measuring
Espionage for better sizing
Espionage for better sizing pt.2

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