I understand this whole-heartedly. I have so many different sizes. At 170, I was wearing a 10 - not tight, but not loose either. Today, (weighed in at 150.4) I am still wearing a 10, but loose. The thing is, I have sizes ranging from 8-13 that I can wear comfortably now...and oddly enough, some of the 8s are bigger than the 13s.

Because of the "vanity sizing" that manufacturers use, I have come to the conclusion that I am not a 'single size' but rather a range.... I wear size 8-13... when I go shopping for pants and such, I always grab the same garment in 3 sizes. Sometimes, I am the smaller, sometimes the middle, and sometimes ALL of them dont fit.

I definitely feel you have to TRY something on because regardless of what the manufacturer says the recommended measurements are, their sewing department disagrees. (either that or they have a sense of humor).