I'm 5'6", 140 lbs, thin build. I bought a 15" neck. I had to trim the sides about 1 inch on each side for a snug fit. I had to do this with my other flight shirts so I knew what I was getting myself into. In general, the shirts hold their shape well. Worst of all, the collar remains plastic inside the shirt and breaks over time. They cannot be replaced without removing the stitches. I have had these shirts for 2 years now and they are still presentable for a private charter.