Your boxing gloves should be large enough to protect your hands without being so heavy and cumbersome that they limit your range of movement and timing. The most important thing though is to ensure that they fit well and feel comfortable to you. Our hands come in all sorts of shapes and sizes, so any guideline is just that, a generic reference as opposed to a precise rule. Let your own comfort be your guide as the more natural and the gloves feel, the more confident you will be wearing them and the better your performance.