I used there measuring guidelines. The size seemed big, but I ordered the size the directions indicated. I ordered this for "posture support/correction as part of therapy for a back spasm as directed by the pain clinic I was referred to. I might as well be wearing a tee shirt. It certainly is comfortable, but does NOTHING for posture support/correction. Who wears that much fabric for comfort? In a smaller, better fitting, size it might be useful but I wouldn't know because I followd their sizing guildlines. Frustrated and disapointed.