This is what some would call a Smedium on me. It's a form fitting, Medium T. I'm 5'10.6" tall and about 185. I wear medium in most shirts and my waist size is 33/34. I was expecting this to fit the way it does but some may consider it a little tight in the chest and arms. In a suit I wear a 42 Regular jacket as a reference to the shoulders/ chest.