I'm 5ft 6in, 140lbs and slim. I bought a 15" neck. I had to trim the sides about 1 inch on each side for a good fit. I had to do this with my other flight shirts so I knew what I was getting into. Generally the shirts keep theirs Shape good Worst of all the collar remains plastic inside the shirt and will break over time They cannot be replaced without removing the stitches I have had these shirts for 2 years now and they are still for a private Charter presentable.