Because I wanted to be on the safe side, I ordered a medium. The sizing guide on their website was helpful (look for the "see how it fits" button), but it doesn't tell you exactly where to measure from. This is actually why I only ordered one shirt for now; I'm guessing the sizing will be similar for all of them. I normally get mediums in fitted shirts, and this one was a little loose on me. Also, the v-neck is deep. But as you can see, I threw a tank top on under it so I felt comfortable wearing it to work. It's long too, but I personally like long shirts. It saves me from doing the Picard manuever all day. The shirt is super soft and only a little sheer. Overall, the quality is top notch and the price is extremely fair for what you receive.
I can't wait to wear this shirt and other Her Universe designs at conventions. I like to wear them in the real world too, but today someone did ask if I was wearing a Twilight shirt. Because Ahsoka and Bella look so much alike. Duh.