Many knitters are frustrated by the amount of time they spend on making what turns out to be a poorly fitting garment. They chose the pattern size to knit based on their bust measurement which doesn't always work. The reason for this is that sizes get larger not with the assumption that bigger sizes carry more body fat or a fuller bust line, but with the assumption that the underlying bone structure is larger. This impacts both the plus size woman as well as the woman who is well endowed. Plus sizes in retail don’t just make things bigger they adjust all the other proportions as well at varying rate of increase. Many knit designers are using the Craft Yarn Council measurements as a guideline. You can check their website for further details. http://craftyarncouncil.com/womansize.html
These measurements are limited, for example there are no neckline standards for designers to follow. They also seem to be based on very tall bodies judging by their armhole depth and back waist measurements. I've wondered if perhaps these are model measurements for samples? Stats Canada says the average woman is 5 ft. 3.4 in. Take note that the sizing charts from the council do not include information about height. Knitting patterns in general assume that front and back proportions are exactly the same but they are not on most people. Our upper arms are bigger at the back, our side to side measurements don’t equal one half our total measurement and the most obvious differences are at the bust lines and tummies and hips.
Arms, armholes and torsos don’t get longer as people get wider but patterns do! The industry expectation is that you lengthen as size increases because sizing assumes a thin body. It’s also easier to wear clothing that is too long rather than items that are too short. Many designers agree that this is wrong but no one has come up with a better alternative. Which is why I think we are struck with the current sizing standards.