Size： "Inner Diameter: 5.2” Outer Diameter: 10.8” Maximum inner diameter stretch: 14.96’’ Please note size is for reference, 0""-0.2 ""error is allowed Instructions： The elastic band fits most head size and most long thick natural hair. But if your hair type is very special such as wild-curl up, this shower cap may not be very perfect. Before using the cap, it’s recommended to secure your hair at the nape of your neck for the best fit.