Take your true dress-shirt collar size. The shirt is cut in European collar sizes and the size menu shows the matching collar in inches: EU 39 is 15.5, 40 is 15.75, 41 is 16, 42 is 16.5, 43 is 17, 44 is 17.5, 45 is 17.75 and 46 is 18. If you sit between sizes or like room to layer a knit over it, take the larger. The collar sits differently from a regular point collar, so if mandarin collars are new to you, come in and try one on. Call 780-431-4293 and we will sort out your size.