These flip-up sunglasses are designed to provide convenient sun protection that can be lifted out of the way when not needed. The flip-up design allows you to move between shaded and bright conditions without removing your glasses, making them a practical option for driving, walking, or outdoor activities. The best way to find the right size flip-up is to measure your glasses in millimeters total width x total height. As a general rule add 2mm's to the height and width to help make up for how the flip-up attaches to your glasses.