First of all, you need to know that frame size is not just the only number, and it is a series of numbers. Let me tell you why. In most cases, you may see some numbers inside of the frame. And they stand for your frame measurement. You have to distinguish they are respectively temple arm length, eye size and nose bridge. And the number of your temple arm length usually ranges from 125 to 145, whose unit is millimeter. Naturally, the rest two numbers are your eye size and your nose bridge size. In most cases, the larger one is your eye size. If you want to get the accurate numbers, you had better get them from a good optical store. Anyway, I wish this could help.