Example: 47 19 130
The first number 47 is the lens diameter.
The second number 19 is the nose bridge width.
The third number 130 is the earpiece length.
Note: Lens height (B Vertical) must be a minimum of 28mm to accommodate a bifocal or multifocal lens.
Note: There is an acceptable deviation of 2mm in these measurements. Therefore, you do not have to be exact.
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.
Frame size is a measurement for the frame. It is the same as your clothe size, shoes size etc. And the frame size is very important for people who order online eyeglasses frame. Since they can't try on the frame, they have no idea if the frame fit for their face. This is why they need read the frame size about the item online. And usually, frame size include lens width, bridge distance, temple length, lens height and total width etc. And all of them are measured by mm. If you want to get suitable frame, you shall buy right sized frame as you pick up shoes according to their sizes and style etc.
The size of your frames can affect the look of the glasses on your face and how comfortable they are to wear: The top edge of the frames should be no higher than the line of your eyebrows. The bridge design and position is the key to a comfortable fit. The lower edge of the frames should not sit on your cheeks, even when you smile, so that they don't rub or irritate. The size should be in proportion to your face - if you have a small face, don't choose large glasses. The width of the frames should not be wider than the overall width of your face at the temples.
To choose a suitable frame, you need to get your prescription first.