The size guides provided by brands are purely just that...guides. Every brand will fit slightly differently, so that is why it is always a good idea to try a few different suits on to make sure they fit well around the neck, chest and arms in particular. From experience, the HUUB suits seem to be quite tight fitting for people with larger chests. Orca suits tend to fit well for people with wider necks! Zone3 seem to be fairly standard fitting as far as UK ???normal??? sizing goes. Not sure about other brands!! Hope that helps!!