Knowing the right measurement for your frames is very important before shopping for glasses online. There is a set of three numbers inside of your frame temple arm, they look like 45-18-143. The first number is your frame width, the second number is the bridge distance and the third number is the temple length. With these numbers, you can select glasses from KoalaEyE that fit you best.
If you do not have those numbers in hand, you can always try measuring by yourself. Just keep this mind, when measuring frame width, you need to measure from temple screw to temple screw. For temple length you need to measure from the temple screw to the temple tip.