The sizing chart XS - XXL (six total sizes) is utilized on garments that are designed to have a very relaxed fit. When garments are more form fitting or a particular fit is desired (such as fitted dress or pants) they will be designed in size numerical 0-22 (12 total sizes) to provide more options for garments that are more fitted.
Taking Your Measurements
The primary measurements you will refer to when taking your measurements are your bust, waist, and, hip. It is very common to incorrectly take measurements due to personal interpretations of where these measurements fall. To help explain the reasoning on how this is done, think of how you need your clothes to fit, you need them to fit over you bust and hips, so you will be taking the measurement of your fullest bust and hips. You also want to a skirt or pant to fit comfortably against your waistline, so in this case you will be taking the measurement of the narrowest part of your waist. When taking your measurements, it is ideal to wear undergarments you prefer to wear with the item of clothing you are purchasing, make sure to keep the measuring tape parallel to the ground, and make sure you are not pulling it too tight.
Need further assistance choosing a size? When between sizes and/or unsure, feel free to consult and ask questions, happy to help!