J'm afraid that the same problems arise with ordinary T-shirts and polo shirts. Sizes vary from company to company and then you have the problems of classic fit, slim fit etc. It's the same with trousers. I'm a 34" waist but buy 32" waist. There's no way I'm a 32" but I think that they label them smaller to make you feel better. The only way to get the right size is to try items on.