How do I find what size I am for eyeglasses?

Question

I see measurements and I know what they are when they say 45 lens-20 bridge-135 temple but how do I find the exact measurements for my head?

Or is the difference between 52 and 53mm lens that big of a deal and should I just try a lot on and take whatever fits. When I'm trying them on will I notice a difference between 1mm?

Answer 1

The sizes are only really an ordering reference, and useful when cutting the Rx lenses to fit the frame.

Two frames reading 48/20 135 can fit totally differently on the face because of features and measurements not specified in those three numbers.  Which is why it's pretty hopeless to order frames off the WWW untried.

Even the overall width of a frame isn't specified in that 45/20, since it only describes the widest point of the lenses, and the narrowest distance between them (Box system, not datum)

Try a lot on and and take what fits and suits, and don't worry about the numbers, except that the numbers on the one you like and the one you finally get should match!