You have a common 10 inches difference between your waist and your hip in circumference, but your measurements don’t correspond to a size on the size chart.
Let’s say, for example, you have a waist measurement of 30″ and a hip measurement of 40″. You are smack dab in between an 8 and a 10. And let me tell you, that one inch can mean the difference between holding your breath or feeling comfortable while wearing your skirt. It also means you could possibly have a blow out of your zipper – something I’ve experienced and its not fun or convenient. Here’s what you need to do:
You’ll take the smaller of the 2 sizes and add 1/4 the additional amount necessary to the side seams (please note that I said 1/4 the additional amount necessary and not 1/4″ – the amount depends on how much you need to add). Only at the side seams – which is the seam that is along the outside of your leg.
Back to the example, your waist and hip size are only 1 inch away from a size 8. All you need is just 1 inch more. You take that 1 inch and divide by 4, because you’ll be affecting 4 seam allowances and that’s 1/4 the additional amount you need, and you have 1/4 inch that needs to be added to the side seams of: Pieces A (skirt front), B (skirt back), F (back waistband), and C, D, or E corresponding to the version you pick. Add the necessary amount before you cut your pattern out using a ruler and a pencil and then go ahead and cut out your new size. Does that make sense? Don’t hesitate to ask if you need help with this.