I made an interesting discovery about sizing, combining the knowledge other pattern designers shared with us and the knowledge I gained making our first pattern. I’ve read something about this before, but I didn’t fully understand at the time. So in case that goes for you too, I’ll explain again here. A lot is said and discussed about the size charts different pattern designers use, whether they are based on actual women and the frustration that comes with not fitting into one size column. My survey showed that 78% of you generally do not fall within one size column, so this is a widespread problem. And one of the factors that are responsible for this, is the way sewing patterns are drafted.
When I was doing research for my own size chart, I found StephC’s very helpful blogpost about the waist/hip ratio. The results from her surveys are based on the measurements from over 300 women. They showed that the ratio increases with size. If you go up in bodyweight, the difference between your waist and hip does not stay the same: the waist increases more than the hip. That means that the ratio for someone with size 4 (W/H = 69/94 cm = 27/37″) is 0.73, but that for size 14, the most common ratio is 0.79 (W/H = 84/107 cm = 33/42″). So if you’d draft patterns based on the actual most common size proportions, you would use these ratios.
However, when you draft patterns and you need to grade them (derive other sizes from one size), and to do this your size chart needs to be proportional. That means that the difference between your hip-waist and waist-bust need to increase and decrease with the same amount. If you don’t do this, you’ll need to draft each size from scratch, which is a lot more work than grading based on one master pattern. Even though every designer puts a lot of work into her sizechart, all size charts show this, as explained by Dixie. This means that, looking at the above examples, when you choose 27/37″, a difference of 10 inches, your larger size can’t be 33/42″ because that would be only 9″ difference. You’ll have to adjust your sizechart, moving it away from the most common size for the practicality of pattern grading, and make it 33/43″. Most designers draft patterns in such a way that it’s easy to cut between sizes and so they have to have only one set of measurements to grade up and down from. An exception is Cake Patterns. She lets you connect the dots on her patterns that correspond with your size, thus customizing the pattern.
Does this clarify things for you? It certainly did for me. If you have any thoughts, questions or corrections on what I’ve explained, please leave a comment!