. . . if I’m going to be buying glasses online? I know obviously my prescription, but there are size measurements too, aren’t there?
Yes, you’ll need your pupil distance. My optometrist couldn’t tell me, but the girls in the eyeglasses store attached to his practice did it with no problem - there’s a little gadget. Took five seconds and they didn’t care that I wasn’t buying from them. Love my online glasses, too!
Have you thought of looking on the online site you wish to use, and see what they ask for? As an example GlassesOnline Help
Only pupillary distance. You might want to try on a few pairs to get the correct eyesize and temple length.
The eyesize will be printed on the arm - it’ll be somewhere around 50 - and then there will be an open square, and the temple length, while will be a hundred and something.