One thing about measuring. Measure your bust and your high bust which is in the armpits above the bust measurement. The above the bust measurement will tell you what size the shoulders need, which in cutting multisize patterns can be a real help. It will also help if you are on the pattern break, if you are a size 24-26 and the pattern runs 18-24 or 26-30 you may want to consider in your choice, if your bust is 26, but your shoulders are 20 you may want to get the smaller pattern for more fitted garments and jut add a little in the bust, but if your shoulders 24 and bust 28 you might want the larger pattern. Also use your hip measuement as a better guide for more fitted pants, and skirts. Taking in a waist band is generally easier than trying to piece together hips.

Actually, the only rhyme or reason is with the pattern companies! Clothing manufacturers make up their own sizing. Many times, if you pay more for something, you can buy a smaller size!