In a typical guys shirt, I wear a small if I want it tight fighting and a medium if I want it a little loose. I bought a medium for the Octohug shirt. The waist fits like a small, but from the chest up it fits like a large. Now, mind you, I'm a C cup so it's not like I'm flat chested. I don't know what body shape this shirt is supposed to fit, but it's definitely not mine. I'm so disappointed. It's such a cute design, but unless I get a boob job this will never fit me right.