An inch or less for ladies, or those with shorter necks. 1.5-2 inches seems to be workably comfy on men though. That particular collar is about 1.5 inches wide (I own it) and I can wear it for a good amount of time, but it is a bit irritating and restrictive (more than just regular collar restrictive, that is) as well as funny lookin' on my smaller frame (5'2", with short everything). My partner, however, looks great in the thing and seems to experience no discomfort unless he is sweating or I tighten it a bit too much.