Generally, we try to approximate XS, Small, Medium, Large, and XL for all of our frames. That said, sometimes a Medium for one person is a Small for another. That's why, in some case, you may see some frames labeled Small/Medium, Medium/Large or Large/XL - as these frames straddle these two sizes. If you're unsure of what size frame you need, you can always take advantage of our Home Try-On policy to check the fit. It's free shipping both ways, so there's nothing to lose.