I normally wear a small or medium top, but after reading the review about the small sizing, I decided to go with the medium. I'm glad I did, otherwise it wouldn't have fit. I can fasten both buttons, but there's not much room. It's a very "fitted" blazer, I'll just say that. The arms are roomy, though. I would have preferred it a little longer. I really like the cut and design, and the price is excellent, but order one size up on your normal size if you're an adult as this is for juniors.