A size chart is the start of choosing motorcycle gloves, not the final answer. Measure your hand against the maker’s guide, then put on both gloves. A good fit feels close and secure without squeezing the palm or restricting finger movement. Your fingertips should come near the ends of the glove fingers. Excess material there can dull the feel of the motorcycle’s controls.
Pay attention to the palm as well. It should lie fairly flat inside the glove, without large folds or pressure points. Grip the handlebars and move your fingers as you would for the throttle, brake and clutch. If the material bunches up or your hand begins to feel numb, the size or shape is wrong even if the label matches your usual number. Protective sections should remain in the intended position as your hand moves.
Material also affects the fit over time. Leather can ease slightly with use, while textile gloves tend to stay closer to their initial shape. That is no reason to buy an obviously tight pair in the hope that it will eventually become comfortable. Choose gloves for the conditions in which you will actually ride, and make sure the wrist closure feels secure without limiting movement.