Find your current frame size
You may also use a pair of sunglasses you currently own to determine your best size. Frame sizing is typically noted on the inside of either temple (see illustration below). The eye/lens size is usually first, then the bridge size, then temple size. Use the eye/lens size to determine the best frame size.
The eye size is typically going to be the most important size for identifying how a pair of sunglasses will look. The eye size number measures the width of the lens, measured from the bridge, in millimeters. The bridge width is the distance between the lenses in millimeters. And the third number is the length of the temple in millimeters.