Not sure about everyone else but I am 160 pounds, 5ft 8 inches tall and in good shape. I run medium in most everything, this is considered a body hugging fit.However, when I washed this shirt in the cold and dried it normally, it came out of the dryer and looked like it would fit my 6 year old son. Unfortunately, if you order a size up, I don't feel like the overall shape of the shirt loses taper on the arms and body, although I'm not sure.