All sunglasses and eyewear have a standardized size measurement system that consists of three numbers printed on the inside of the left temple which represents the size. These numbers are written in millimeters for more accuracy. What do the numbers mean? All sunglasses and eyewear have a standardized three number size code. This code is found on the inside of the left arm of the sunglasses. An example of what a size code looks like is below. The size of the sunglasses on the above is 62-10-140. The first number is called the âeyeâ and is the distance across one lens.