Your shoe size is ingrained in the back of your head, you know how different brands fit and whether you should size up or down on something with a Lunar sole versus a Chuck Taylor. So you have no reason to not pay the same attention to your measurements either. It's not that hard, you can go to a tailor to do it for you, or just get a tape measure and do it yourself. The most important measurements will be your shoulders, chest, arm length, and waist. Armed with that knowledge, you'll be better equipped to get clothes that actually fit.