If you're a young teen (or the parent of one), trying to determine your correct clothing size can be difficult, especially if you're stranded between the girls' section and the juniors' section of the department store. But a glance at a size conversion chart can help you estimate the right fit.
Look at the size tag on an article of clothing that fits well, whether in junior or girls' sizes. For an example, if you have a size 14 girls' dress that fits well, you may want to know its equivalent in a junior size.
Check a size chart that includes measurements for chest, waist and hips, such as the one from Simplicity patterns (sewingpatterns.com), or one from your favorite clothing company. You don't have to know the measurements exactly, but it will help you to estimate the size. In the example, a size 14 lists measurements as chest: 32 inches, waist: 26 1/2 inches, and hips: 34 inches.
Take the measurements you found in the last step and look for corresponding measurements in the other size table. For example, looking at the junior chart, you can see that a girls' size 14 falls squarely between junior sizes 7 and 11, so we'll estimate that it's the equivalent of a size 9. Note that it is not an exact equivalent. A junior size 9 can have hips as wide 35 inches and a waist as wide as 25 inches.
A girl who is 10 or 11 and is a little more developed can begin wearing junior sizes if they suit her better. Likewise, a girl whose body is a little slower to develop can continue wearing girls' sizes if she prefers. The key is fit, not age.
Size conversion is not an exact science. For the most accurate fit, you need to try on articles of clothing before you buy them. If that's not possible, use a tape measure and take accurate measurements of bust, hips and waist of an article of clothing that fits you well, then match them to the specific size chart of the brand of clothing you plan to buy.