Your waist size takes priority over the other measurements. If all your measurements do not fall in the same size, then use the size your waist measures at for the best fit. Some of your measurements may be in between sizes, take the higher size for a comfort fit.
HOW DO I MEASURE MYSELF?
This one is easy! Find your most comfortable pants and check the labeled size!
Measuring your waist is best done with your clothes off. Simply wrap a tape measure around your stomach. Be sure to cover your belly button, this insures you're measuring the correct part of the waist.
This part is also best done without any clothes on. Bring your feet side by side, and wrap the measuring tape around the widest part of your hips. Remember, for the most accurate size, the tape measure needs to include the biggest part of your butt as well!