LensCovers are perfect for anyone who wants the benefits of sun protection while wearing their prescription glasses. They're lightweight and easy to slip on over your prescription glasses. You'll want to keep a pair in the car, office, house or wherever you need them! LensCovers are designed to wrap around your face blocking the sun from the side as well; a practical alternative to expensive prescription sunglasses! LensCovers are polarized, providing increased clarity, reduced eye fatigue, and glare protection. How to measure your prescription frames for LensCover sunglasses: 1- Measure the widest part of your prescription frames left to right, this is the "width". Next measure the height of the lens with frame included. 2- Choose the LensCover frame (below) that is slightly larger in width and height than your frame measurements. LensCovers Extra Small is 4-15/16 inches x 1-1/2 inches high LensCovers Small is 5-5/16 inches wide x 1-5/8 inches high LensCovers Medium is 5-1/2 inches wide x 1-3/4 inches high LensCovers Large Slim is 5-11/16 inches wide x 1-7/8 inches high LensCovers Large is 5-3/4 inches wide x 2-1/8 inches high For example, if your prescription frames measure 5-1/4 inches (width) x 1-1/4 inches (height), the correct LensCovers Frame would be size Small. Hard Case for LensCovers are available under a separate listing.