If you're in between sizes, it will depend on how you like your suit to fit. A rule of thumb is that unless you are sure you want your suit to fit very tightly, size up if you are between sizes. More than 80% of our returns are for a larger size.
Note you will probably have a hard time zipping up a suit that's the right size for you. This doesn't mean it's the wrong size. Once you have the suit zipped up and you hop in the water, it should loosen up. We highly recommend that you swim in your suit before making a final decision on fit. Of course, if you're not happy with the fit you can return it for another size within 30 days.