It is common to fall between different sizes depending on your proportions. For example, you may find you have a size 18 bust, a size 16 waist, and a size 14 hip. This is perfectly normal! For the best fitting results, it is best practice to "grade" between sizes, which means connecting all those sizes on your pattern before cutting it out.
Grading between sizes is imperative when you are making pants and fitted garments. If you just cut out one straight size, you'll have to make substantial fitting adjustments after the fact to get the garment to fit you correctly everywhere else - grading saves you time and headaches.
With that said, not all garments need to be graded all the time. For example, a looser-fitting dress like our Charlie Caftan has lots of ease through the hips. In this case you would use your bust measurement as your base size and skip grading through the waist and hip since there is lots of room even if your hip is several sizes larger. When in doubt, check the finished garment measurements to see if you'll have the space you need.
For more help grading between sizes, please visit our blog post on Choosing a size and Grading Between sizes.