That's mostly dependent on body type, carry position and the holster being used. I carry a Glock 19 sized pistol in the AIWB position. I don't wear baggy shirts and it conceals just fine. If a person is bigger around at the belt line than they are at the shoulders and chest, that's going to make it a lot harder. All I can say is that, for a person who isn't fat, concealing a Glock 19 or similar is absolutely doable with little or no wardrobe change. I do it and a know a dozen or more other guys who do it.