If you're the kinda gal that's always wishing she ordered a size smaller, then this is your jacket for sure. I often end up ordering kids' sizes but I took a chance on this because another customer's review was that they run small so I ordered the extra small (adult size) and I wouldn't want it to be a single inch smaller anywhere. In fact, the hood is a bit tiny (I won't get started on the accusations of my friends that I have a large head for my body size haha) but it doesn't bother me much. The reason I've worn this thing every day since I got it (yeah, even in the office) is the thumb holes and the perfect arm length. The thermal is great but not overwhelming and it's the perfect weight to wear to and from the gym so you feel like you're not gonna get pneumonia but you're not grossed out swimming in your sweaty hoodie.