EYEGLASSES: Buying the right size online?

If you don't have to buy the glasses right this instant, go to a drugstore, Walmarts or wherever and try on some knock-off Wayfarer style sunglasses and see how they fit. Particularly where they cross your nose, as the bridge size is quite a bit bigger then what you are wearing and it is hard to adjust the bridge size for plastic frames if they aren't right. The copies might not have exactly the same shape but will be close enough the see how they would fit on you. Might save you from making an expensive mistake.