I wear a size 6 with a 31" waste. But, I have 39 1/2" hips so things tend to fit pretty well. If I were you, I would go to a store and try some on. Probably start with a size 5 and work from there. You can find the odd sizes in the misses (teen) section. Women's sizes vary depending on the make, fabric, cut, day of the week, hour...just about every combination of factors. It is quite difficult to find pants that fit perfectly. Also, unless they are low rise, they are made to be worn around the waste, not hips. That will have a factor on how they fit. Good luck.